From 06f4e11d3f955071d470d9263e1cee70b77964cf Mon Sep 17 00:00:00 2001
From: daniel_huang <159147443+Danielncku@users.noreply.github.com>
Date: Thu, 1 Oct 2026 22:00:27 +0800
Subject: [PATCH 1/3] Add local topic filtering

Expose problem topics as local card metadata so candidates can narrow
the lobby without revealing tags on each card. Keep recommendations
inside the selected topic and cover combined filters in unit and browser
tests.
---
 scripts/gen-problem-cards.py            |  18 +-
 tests/browser/dom.js                    |  15 +-
 tests/browser/lobby-render.test.js      |   9 +-
 tests/browser/lobby.test.js             |  31 +++
 tests/browser/practice-insights.test.js |  32 +++
 web/app.js                              |  75 +++++-
 web/index.html                          | 315 ++++++++++++------------
 web/practice-insights.js                |  16 ++
 web/styles.css                          |  42 +++-
 9 files changed, 388 insertions(+), 165 deletions(-)
 create mode 100644 tests/browser/practice-insights.test.js
 create mode 100644 web/practice-insights.js

diff --git a/scripts/gen-problem-cards.py b/scripts/gen-problem-cards.py
index e6134eac..14b23b39 100644
--- a/scripts/gen-problem-cards.py
+++ b/scripts/gen-problem-cards.py
@@ -37,22 +37,24 @@ def parse_args() -> argparse.Namespace:
 
 
 def read_json(path: Path) -> object:
-    return json.loads(path.read_text())
+    return json.loads(path.read_text(encoding="utf-8"))
 
 
 def card(problem: dict[str, object], page: str, title: str) -> str:
     """One lobby card, named the way the interview will name the exercise.
 
-    Keyed by page name, with the scenario title and no topic tags: the
+    Keyed by page name, with the scenario title and topic metadata: the
     recommendation line reads the title off this card, and "Recommended: Coin
     Change", a `coin-change` key or a "Dynamic Programming" tag tells the
-    candidate what they are about to be asked. The published title is not in
-    the page at all; the source slot is filled from the page map only when the
-    candidate turns that on to drill one problem by name.
+    candidate what they are about to be asked. Topics stay in data attributes
+    for local filtering and are not rendered on the card. The published title
+    is not in the page at all; the source slot is filled from the page map only
+    when the candidate turns that on to drill one problem by name.
     """
+    topics = "|".join(str(topic) for topic in problem.get("topics", []))
     return "\n".join(
         [
-            f'  <button class="problem-card" type="button" data-problem="{html.escape(page)}" data-difficulty="{html.escape(problem["difficulty"])}">',
+            f'  <button class="problem-card" type="button" data-problem="{html.escape(page)}" data-difficulty="{html.escape(problem["difficulty"])}" data-topics="{html.escape(topics)}">',
             f'    <span class="problem-title">{html.escape(title)}</span>',
             '    <span class="problem-source" hidden></span>',
             f'    <span class="problem-meta">{html.escape(problem["difficulty"])}</span>',
@@ -79,7 +81,7 @@ def generated(problems: list) -> str:
 
 def main() -> int:
     args = parse_args()
-    html_text = INDEX.read_text()
+    html_text = INDEX.read_text(encoding="utf-8")
     opening = re.search(
         rf"^([ \t]*){re.escape(START)}[ \t]*$", html_text, flags=re.MULTILINE
     )
@@ -113,7 +115,7 @@ def main() -> int:
         return 0
 
     if updated != html_text:
-        INDEX.write_text(updated)
+        INDEX.write_text(updated, encoding="utf-8")
         print(f"updated {len(problems)} problem cards in web/index.html")
     return 0
 
diff --git a/tests/browser/dom.js b/tests/browser/dom.js
index 1adc03ca..fa0558b8 100644
--- a/tests/browser/dom.js
+++ b/tests/browser/dom.js
@@ -334,7 +334,20 @@ export function installDocument(markup) {
   // `#start` and `button#start` render into two different places, which is a
   // page a browser cannot produce.
   const node = (element) => {
-    if (!nodes.has(element)) nodes.set(element, new Element(element.tag));
+    if (!nodes.has(element)) {
+      const created = new Element(element.tag);
+      for (const [name, value] of Object.entries(element.attributes)) {
+        if (name.startsWith("data-")) {
+          const key = name
+            .slice(5)
+            .replace(/-([a-z])/g, (_, letter) => letter.toUpperCase());
+          created.dataset[key] = value;
+        }
+      }
+      if ("value" in element.attributes)
+        created.value = element.attributes.value;
+      nodes.set(element, created);
+    }
     return nodes.get(element);
   };
   globalThis.document = {
diff --git a/tests/browser/lobby-render.test.js b/tests/browser/lobby-render.test.js
index 16ab4f76..c926cb47 100644
--- a/tests/browser/lobby-render.test.js
+++ b/tests/browser/lobby-render.test.js
@@ -46,6 +46,7 @@ const SIGNED_OUT = {
   start: "Start interview",
   "progress-summary": "Could not load progress saved on this device.",
 };
+const PROBLEM_FILTERS = new Set(["problem-topic", "problem-filter-summary"]);
 
 test("the lobby page loads outside a browser and says what it was given", () => {
   for (const [id, expected] of Object.entries(SIGNED_OUT)) {
@@ -62,7 +63,13 @@ test("no other panel of the lobby speaks before anything has loaded", () => {
   const spoke = [];
   for (const [, id] of markup.matchAll(/id="([^"]+)"/g)) {
     const node = dom.node(id);
-    if (node && node.spoken().length && !(id in SIGNED_OUT)) spoke.push(id);
+    if (
+      node &&
+      node.spoken().length &&
+      !(id in SIGNED_OUT) &&
+      !PROBLEM_FILTERS.has(id)
+    )
+      spoke.push(id);
   }
   assert.deepEqual(
     spoke,
diff --git a/tests/browser/lobby.test.js b/tests/browser/lobby.test.js
index 2f82c9e6..8d4a7b79 100644
--- a/tests/browser/lobby.test.js
+++ b/tests/browser/lobby.test.js
@@ -362,6 +362,37 @@ lobbyTest(
   { viewport: { width: 1280, height: 800 } },
 );
 
+lobbyTest(
+  "topic and difficulty filters narrow the problem cards together",
+  async (page) => {
+    await lobby(page);
+    await page.click("details.problem-picker summary");
+
+    await page.selectOption("#problem-topic", "Array");
+    const filtered = await page
+      .locator("[data-problem]:visible")
+      .evaluateAll((cards) =>
+        cards.map((card) => ({
+          difficulty: card.dataset.difficulty,
+          topics: card.dataset.topics.split("|"),
+        })),
+      );
+    assert.ok(filtered.length > 0, "the topic filter hid every problem");
+    assert.ok(
+      filtered.every(
+        (card) => card.difficulty === "Medium" && card.topics.includes("Array"),
+      ),
+      "a visible card did not match both filters",
+    );
+
+    await page.click("#problem-filters-reset");
+    assert.ok(
+      (await page.locator("[data-problem]:visible").count()) > filtered.length,
+      "reset did not restore the other Medium problems",
+    );
+  },
+);
+
 lobbyTest(
   "a candidate who touches nothing gets the server's own default length",
   async (page) => {
diff --git a/tests/browser/practice-insights.test.js b/tests/browser/practice-insights.test.js
new file mode 100644
index 00000000..b0b969fc
--- /dev/null
+++ b/tests/browser/practice-insights.test.js
@@ -0,0 +1,32 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import {
+  availableTopics,
+  filterProblems,
+} from "../../web/practice-insights.js";
+
+const problems = [
+  { id: "a", difficulty: "Easy", topics: ["Array", "Hash Table"] },
+  { id: "b", difficulty: "Medium", topics: ["Array", "Sorting"] },
+  { id: "c", difficulty: "Hard", topics: ["Graph"] },
+];
+
+test("topics are unique and sorted", () => {
+  assert.deepEqual(availableTopics(problems), [
+    "Array",
+    "Graph",
+    "Hash Table",
+    "Sorting",
+  ]);
+});
+
+test("difficulty and topic filters combine", () => {
+  assert.deepEqual(
+    filterProblems(problems, {
+      difficulties: new Set(["Medium", "Hard"]),
+      topic: "Array",
+    }).map((problem) => problem.id),
+    ["b"],
+  );
+});
diff --git a/web/app.js b/web/app.js
index 7a90d634..ce1f9ae1 100644
--- a/web/app.js
+++ b/web/app.js
@@ -19,6 +19,7 @@ import {
 import { reportMarkdown, reportMarkup } from "./render.js";
 import { downloadMarkdown, reportFilename } from "./download.js";
 import { loadPageMap } from "./problem-data.js";
+import { availableTopics, filterProblems } from "./practice-insights.js";
 import {
   parseGroundingFile,
   retainedSelection,
@@ -104,6 +105,9 @@ const nodes = {
   groundingClear: document.querySelector("#grounding-clear"),
   groundingError: document.querySelector("#grounding-error"),
   durationNote: document.querySelector("#duration-note"),
+  problemTopic: document.querySelector("#problem-topic"),
+  problemFiltersReset: document.querySelector("#problem-filters-reset"),
+  problemFilterSummary: document.querySelector("#problem-filter-summary"),
 };
 
 // Every card carries the pressed state from the start, not only the one that
@@ -113,6 +117,9 @@ const cards = [...document.querySelectorAll("[data-problem]")].map(
   (button) => ({
     id: button.dataset.problem,
     difficulty: button.dataset.difficulty,
+    topics: String(button.dataset.topics || "")
+      .split("|")
+      .filter(Boolean),
     button,
   }),
 );
@@ -159,6 +166,20 @@ showSources.addEventListener("change", () => {
 });
 void applySources();
 const levels = [...document.querySelectorAll('[name="difficulty"]')];
+const TOPIC_KEY = "codetrial.problemTopic";
+const topics = availableTopics(cards);
+for (const topic of topics) {
+  const option = document.createElement("option");
+  option.value = topic;
+  option.textContent = topic;
+  nodes.problemTopic.append(option);
+}
+try {
+  const storedTopic = localStorage.getItem(TOPIC_KEY) ?? "";
+  if (topics.includes(storedTopic)) nodes.problemTopic.value = storedTopic;
+} catch {
+  /* the filter still works for this visit */
+}
 
 // A picked card is a choice about this one interview, not about the filter the
 // checkboxes carry, so it leaves them alone. It suggests a length to go with
@@ -213,6 +234,25 @@ for (const input of levels) {
   });
 }
 
+nodes.problemTopic.addEventListener("change", () => {
+  try {
+    localStorage.setItem(TOPIC_KEY, nodes.problemTopic.value);
+  } catch {
+    /* the filter still works for this visit */
+  }
+  filterSelectionChanged();
+});
+
+nodes.problemFiltersReset.addEventListener("click", () => {
+  nodes.problemTopic.value = "";
+  try {
+    localStorage.removeItem(TOPIC_KEY);
+  } catch {
+    /* the filter still resets for this visit */
+  }
+  filterSelectionChanged();
+});
+
 let grounding = { requirements: [], skills: [], anchors: [] };
 const groundingReads = { jd: 0, resume: 0 };
 
@@ -870,11 +910,40 @@ function applyDifficulties() {
   const difficulties = selectedDifficulties();
   // The picker is a shortcut to one problem, not a second copy of the wall the
   // checkboxes just hid, so it shows what the checkboxes selected.
-  for (const card of cards)
-    card.button.hidden = !difficulties.has(card.difficulty);
+  applyProblemFilters(difficulties);
   setDuration(suggestedDuration(difficulties));
 }
 
+function topicEligibleCards() {
+  return filterProblems(cards, { topic: nodes.problemTopic.value });
+}
+
+function applyProblemFilters(difficulties = selectedDifficulties()) {
+  const visible = new Set(
+    filterProblems(cards, {
+      difficulties,
+      topic: nodes.problemTopic.value,
+    }),
+  );
+  for (const card of cards) card.button.hidden = !visible.has(card);
+  const topic = nodes.problemTopic.value;
+  nodes.problemFilterSummary.textContent = `${visible.size} problem${visible.size === 1 ? "" : "s"}${topic ? ` tagged ${topic}` : ""} shown.`;
+}
+
+function filterSelectionChanged() {
+  const eligible = new Set(topicEligibleCards());
+  applyProblemFilters();
+  if (manualProblem && eligible.has(problem)) return;
+  manualProblem = false;
+  roll = Math.random();
+  avoidedProblem = undefined;
+  if (historyReady) recommend();
+  else {
+    setProblem(null);
+    nodes.recommendation.textContent = "";
+  }
+}
+
 /// `note` is the sentence explaining a level the reports chose, empty when the
 /// candidate chose it themselves and so already knows.
 function recommend(note = "") {
@@ -883,7 +952,7 @@ function recommend(note = "") {
   // they had just selected.
   if (manualProblem) return;
   const choice = pickProblem(
-    cards,
+    topicEligibleCards(),
     selectedDifficulties(),
     reports,
     () => roll,
diff --git a/web/index.html b/web/index.html
index c8a35caf..e6782c74 100644
--- a/web/index.html
+++ b/web/index.html
@@ -77,760 +77,773 @@ <h1>Practice a live technical interview</h1>
           on each card, for drilling one by name. The interview names it in
           small print either way.</label
         >
+        <fieldset class="practice-filters">
+          <legend>Filter problems</legend>
+          <label for="problem-topic">Topic</label>
+          <select id="problem-topic">
+            <option value="">All topics</option>
+          </select>
+          <button id="problem-filters-reset" type="button">Reset filter</button>
+          <p
+            id="problem-filter-summary"
+            class="muted small"
+            aria-live="polite"
+          ></p>
+        </fieldset>
         <!-- prettier-ignore -->
         <section class="problem-grid" aria-label="Problems">
           <!-- Generated by scripts/gen-problem-cards.py from problem-bank/. Do not edit by hand. -->
-          <button class="problem-card" type="button" data-problem="template-delimiter-audit" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="template-delimiter-audit" data-difficulty="Easy" data-topics="String|Stack">
             <span class="problem-title">Template Delimiter Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="chargeback-pair-match" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="chargeback-pair-match" data-difficulty="Easy" data-topics="Array|Hash Table">
             <span class="problem-title">Chargeback Pair Match</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="firmware-buffer-splice" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="firmware-buffer-splice" data-difficulty="Easy" data-topics="Array|Two Pointers|Sorting">
             <span class="problem-title">Firmware Buffer Splice</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="muted-alert-filter" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="muted-alert-filter" data-difficulty="Easy" data-topics="Array|Two Pointers">
             <span class="problem-title">Muted Alert Filter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="telemetry-reading-dedupe" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="telemetry-reading-dedupe" data-difficulty="Easy" data-topics="Array|Two Pointers">
             <span class="problem-title">Telemetry Reading Dedupe</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="alert-digest-trimming" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="alert-digest-trimming" data-difficulty="Medium" data-topics="Array|Two Pointers">
             <span class="problem-title">Alert Digest Trimming</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="replica-quorum-version" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="replica-quorum-version" data-difficulty="Easy" data-topics="Array|Hash Table|Divide and Conquer|Counting">
             <span class="problem-title">Replica Quorum Version</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="carousel-slot-shift" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="carousel-slot-shift" data-difficulty="Medium" data-topics="Array|Math|Two Pointers">
             <span class="problem-title">Carousel Slot Shift</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="single-resale-window" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="single-resale-window" data-difficulty="Easy" data-topics="Array|Dynamic Programming">
             <span class="problem-title">Single Resale Window</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="single-slot-reseller" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="single-slot-reseller" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Greedy">
             <span class="problem-title">Single Slot Reseller</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="relay-chain-reachability" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="relay-chain-reachability" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Greedy">
             <span class="problem-title">Relay Chain Reachability</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="drone-pad-hopping" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="drone-pad-hopping" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Greedy">
             <span class="problem-title">Drone Pad Hopping</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="package-impact-score" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="package-impact-score" data-difficulty="Medium" data-topics="Array|Sorting|Counting Sort">
             <span class="problem-title">Package Impact Score</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="backend-pool-sampler" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="backend-pool-sampler" data-difficulty="Medium" data-topics="Array|Hash Table|Math|Design|Randomized">
             <span class="problem-title">Backend Pool Sampler</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="pipeline-stage-gains" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="pipeline-stage-gains" data-difficulty="Medium" data-topics="Array|Prefix Sum">
             <span class="problem-title">Pipeline Stage Gains</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="circular-route-charging" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="circular-route-charging" data-difficulty="Medium" data-topics="Array|Greedy">
             <span class="problem-title">Circular Route Charging</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shift-crew-bonus-points" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="shift-crew-bonus-points" data-difficulty="Hard" data-topics="Array|Greedy">
             <span class="problem-title">Shift Crew Bonus Points</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="terrain-runoff-pooling" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="terrain-runoff-pooling" data-difficulty="Hard" data-topics="Array|Two Pointers|Dynamic Programming|Stack|Monotonic Stack">
             <span class="problem-title">Terrain Runoff Pooling</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="archive-volume-numbers" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="archive-volume-numbers" data-difficulty="Easy" data-topics="Hash Table|Math|String">
             <span class="problem-title">Archive Volume Numbers</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="film-credits-year-stamp" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="film-credits-year-stamp" data-difficulty="Medium" data-topics="Hash Table|Math|String">
             <span class="problem-title">Film Credits Year Stamp</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="autocomplete-token-width" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="autocomplete-token-width" data-difficulty="Easy" data-topics="String">
             <span class="problem-title">Autocomplete Token Width</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="metric-namespace-root" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="metric-namespace-root" data-difficulty="Easy" data-topics="String|Trie">
             <span class="problem-title">Metric Namespace Root</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="backwards-caption-repair" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="backwards-caption-repair" data-difficulty="Medium" data-topics="String|Two Pointers">
             <span class="problem-title">Backwards Caption Repair</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="bouncing-print-head" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="bouncing-print-head" data-difficulty="Medium" data-topics="String">
             <span class="problem-title">Bouncing Print Head</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="firmware-signature-scan" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="firmware-signature-scan" data-difficulty="Easy" data-topics="Two Pointers|String|String Matching">
             <span class="problem-title">Firmware Signature Scan</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="thermal-receipt-layout" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="thermal-receipt-layout" data-difficulty="Hard" data-topics="Array|String|Simulation">
             <span class="problem-title">Thermal Receipt Layout</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="mirror-phrase-contest-filter" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="mirror-phrase-contest-filter" data-difficulty="Easy" data-topics="Two Pointers|String">
             <span class="problem-title">Mirror Phrase Contest Filter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="ordered-event-trace-check" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="ordered-event-trace-check" data-difficulty="Easy" data-topics="Two Pointers|String|Dynamic Programming">
             <span class="problem-title">Ordered Event Trace Check</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="billboard-pole-banner" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="billboard-pole-banner" data-difficulty="Medium" data-topics="Array|Two Pointers|Greedy">
             <span class="problem-title">Billboard Pole Banner</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="gift-card-bundle-pair" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="gift-card-bundle-pair" data-difficulty="Medium" data-topics="Array|Two Pointers|Binary Search">
             <span class="problem-title">Gift Card Bundle Pair</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="ledger-cancellation-groups" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="ledger-cancellation-groups" data-difficulty="Medium" data-topics="Array|Two Pointers|Sorting">
             <span class="problem-title">Ledger Cancellation Groups</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="firmware-checksum-settling" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="firmware-checksum-settling" data-difficulty="Easy" data-topics="Hash Table|Math|Two Pointers">
             <span class="problem-title">Firmware Checksum Settling</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="distinct-keystroke-stretch" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="distinct-keystroke-stretch" data-difficulty="Medium" data-topics="Hash Table|String|Sliding Window">
             <span class="problem-title">Distinct Keystroke Stretch</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="required-marker-span" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="required-marker-span" data-difficulty="Hard" data-topics="Hash Table|String|Sliding Window">
             <span class="problem-title">Required Marker Span</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="packet-chunk-block-offsets" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="packet-chunk-block-offsets" data-difficulty="Hard" data-topics="Hash Table|String|Sliding Window">
             <span class="problem-title">Packet Chunk Block Offsets</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shortest-upload-batch" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="shortest-upload-batch" data-difficulty="Medium" data-topics="Array|Binary Search|Sliding Window|Prefix Sum">
             <span class="problem-title">Shortest Upload Batch</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="puzzle-grid-save-check" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="puzzle-grid-save-check" data-difficulty="Medium" data-topics="Array|Hash Table|Matrix">
             <span class="problem-title">Puzzle Grid Save Check</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="led-panel-ring-scan" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="led-panel-ring-scan" data-difficulty="Medium" data-topics="Array|Matrix|Simulation">
             <span class="problem-title">LED Panel Ring Scan</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sensor-frame-quarter-turn" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="sensor-frame-quarter-turn" data-difficulty="Medium" data-topics="Array|Math|Matrix">
             <span class="problem-title">Sensor Frame Quarter Turn</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="faulty-sensor-grid-blanking" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="faulty-sensor-grid-blanking" data-difficulty="Medium" data-topics="Array|Hash Table|Matrix">
             <span class="problem-title">Faulty Sensor Grid Blanking</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="microbe-culture-tick" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="microbe-culture-tick" data-difficulty="Medium" data-topics="Array|Matrix|Simulation">
             <span class="problem-title">Microbe Culture Tick</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="marquee-letter-tiles" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="marquee-letter-tiles" data-difficulty="Easy" data-topics="Hash Table|String|Counting">
             <span class="problem-title">Marquee Letter Tiles</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="anonymizer-substitution-audit" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="anonymizer-substitution-audit" data-difficulty="Easy" data-topics="Hash Table|String">
             <span class="problem-title">Anonymizer Substitution Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="log-line-shape-template" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="log-line-shape-template" data-difficulty="Easy" data-topics="Hash Table|String">
             <span class="problem-title">Log Line Shape Template</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="scrambled-label-match" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="scrambled-label-match" data-difficulty="Easy" data-topics="Hash Table|String|Sorting">
             <span class="problem-title">Scrambled Label Match</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="letter-rack-clusters" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="letter-rack-clusters" data-difficulty="Medium" data-topics="Array|Hash Table|String|Sorting">
             <span class="problem-title">Letter Rack Clusters</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="recent-card-repeat-alert" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="recent-card-repeat-alert" data-difficulty="Easy" data-topics="Array|Hash Table|Sliding Window">
             <span class="problem-title">Recent Card Repeat Alert</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="allocated-port-block" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="allocated-port-block" data-difficulty="Medium" data-topics="Array|Hash Table|Union Find">
             <span class="problem-title">Allocated Port Block</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="rack-slot-range-labels" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="rack-slot-range-labels" data-difficulty="Easy" data-topics="Array">
             <span class="problem-title">Rack Slot Range Labels</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="room-booking-busy-blocks" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="room-booking-busy-blocks" data-difficulty="Medium" data-topics="Array">
             <span class="problem-title">Room Booking Busy Blocks</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="batch-health-check-windows" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="batch-health-check-windows" data-difficulty="Medium" data-topics="Array|Greedy|Sorting">
             <span class="problem-title">Batch Health Check Windows</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="upload-location-normalizer" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="upload-location-normalizer" data-difficulty="Medium" data-topics="String|Stack">
             <span class="problem-title">Upload Location Normalizer</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="tentative-bid-ledger" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="tentative-bid-ledger" data-difficulty="Medium" data-topics="Stack|Design">
             <span class="problem-title">Tentative Bid Ledger</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="pricing-rule-bytecode" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="pricing-rule-bytecode" data-difficulty="Medium" data-topics="Array|Math|Stack">
             <span class="problem-title">Pricing Rule Bytecode</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="budget-sheet-formulas" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="budget-sheet-formulas" data-difficulty="Hard" data-topics="Math|String|Stack|Recursion">
             <span class="problem-title">Budget Sheet Formulas</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="workflow-handoff-loop" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="workflow-handoff-loop" data-difficulty="Easy" data-topics="Hash Table|Linked List|Two Pointers">
             <span class="problem-title">Workflow Handoff Loop</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="odometer-digit-chains" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="odometer-digit-chains" data-difficulty="Medium" data-topics="Linked List|Math|Recursion">
             <span class="problem-title">Odometer Digit Chains</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="replica-event-interleave" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="replica-event-interleave" data-difficulty="Easy" data-topics="Linked List|Recursion">
             <span class="problem-title">Replica Event Interleave</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="outline-snapshot-duplicator" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="outline-snapshot-duplicator" data-difficulty="Medium" data-topics="Hash Table|Linked List">
             <span class="problem-title">Outline Snapshot Duplicator</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="playlist-segment-flip" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="playlist-segment-flip" data-difficulty="Medium" data-topics="Linked List">
             <span class="problem-title">Playlist Segment Flip</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="radio-frame-batching" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="radio-frame-batching" data-difficulty="Hard" data-topics="Linked List|Recursion">
             <span class="problem-title">Radio Frame Batching</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="activity-feed-retraction" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="activity-feed-retraction" data-difficulty="Medium" data-topics="Linked List|Two Pointers">
             <span class="problem-title">Activity Feed Retraction</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="single-scan-badge-filter" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="single-scan-badge-filter" data-difficulty="Medium" data-topics="Linked List|Two Pointers">
             <span class="problem-title">Single Scan Badge Filter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="playlist-tail-wraparound" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="playlist-tail-wraparound" data-difficulty="Medium" data-topics="Linked List|Two Pointers">
             <span class="problem-title">Playlist Tail Wraparound</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="print-queue-triage" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="print-queue-triage" data-difficulty="Medium" data-topics="Linked List|Two Pointers">
             <span class="problem-title">Print Queue Triage</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="edge-thumbnail-store" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="edge-thumbnail-store" data-difficulty="Medium" data-topics="Hash Table|Linked List|Design">
             <span class="problem-title">Edge Thumbnail Store</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="fraud-rule-worst-case" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="fraud-rule-worst-case" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
             <span class="problem-title">Fraud Rule Worst Case</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="staging-drift-check" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="staging-drift-check" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
             <span class="problem-title">Staging Drift Check</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="right-to-left-layout" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="right-to-left-layout" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
             <span class="problem-title">Right To Left Layout</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="kiosk-panel-mirror-audit" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="kiosk-panel-mirror-audit" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
             <span class="problem-title">Kiosk Panel Mirror Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="crash-dump-index-rebuild" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="crash-dump-index-rebuild" data-difficulty="Medium" data-topics="Array|Hash Table|Divide and Conquer|Tree|Binary Tree">
             <span class="problem-title">Crash Dump Index Rebuild</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="query-parse-cache-restore" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="query-parse-cache-restore" data-difficulty="Medium" data-topics="Array|Hash Table|Divide and Conquer|Tree|Binary Tree">
             <span class="problem-title">Query Parse Cache Restore</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="org-chart-row-navigation" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="org-chart-row-navigation" data-difficulty="Medium" data-topics="Linked List|Tree|DFS|BFS|Binary Tree">
             <span class="problem-title">Org Chart Row Navigation</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="screen-reader-menu-chain" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="screen-reader-menu-chain" data-difficulty="Medium" data-topics="Linked List|Stack|Tree|DFS|Binary Tree">
             <span class="problem-title">Screen Reader Menu Chain</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="dungeon-route-budget" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="dungeon-route-budget" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
             <span class="problem-title">Dungeon Route Budget</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="menu-extension-checksum" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="menu-extension-checksum" data-difficulty="Medium" data-topics="Tree|DFS|Binary Tree">
             <span class="problem-title">Menu Extension Checksum</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="grid-segment-net-yield" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="grid-segment-net-yield" data-difficulty="Hard" data-topics="Dynamic Programming|Tree|DFS|Binary Tree">
             <span class="problem-title">Grid Segment Net Yield</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="ordered-index-cursor" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="ordered-index-cursor" data-difficulty="Medium" data-topics="Stack|Tree|Design|Binary Search Tree|Binary Tree|Iterator">
             <span class="problem-title">Ordered Index Cursor</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="heap-slot-census" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="heap-slot-census" data-difficulty="Medium" data-topics="Binary Search|Bit Manipulation|Tree|Binary Tree">
             <span class="problem-title">Heap Slot Census</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shared-approver-lookup" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="shared-approver-lookup" data-difficulty="Medium" data-topics="Tree|DFS|Binary Tree">
             <span class="problem-title">Shared Approver Lookup</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="collapsed-panel-labels" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="collapsed-panel-labels" data-difficulty="Medium" data-topics="Tree|DFS|BFS|Binary Tree">
             <span class="problem-title">Collapsed Panel Labels</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="hop-depth-signal-means" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="hop-depth-signal-means" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
             <span class="problem-title">Hop Depth Signal Means</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="rollout-wave-planner" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="rollout-wave-planner" data-difficulty="Medium" data-topics="Tree|BFS|Binary Tree">
             <span class="problem-title">Rollout Wave Planner</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="serpentine-tier-sweep" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="serpentine-tier-sweep" data-difficulty="Medium" data-topics="Tree|BFS|Binary Tree">
             <span class="problem-title">Serpentine Tier Sweep</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="tightest-channel-spacing" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="tightest-channel-spacing" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Search Tree|Binary Tree">
             <span class="problem-title">Tightest Channel Spacing</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="latency-rank-query" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="latency-rank-query" data-difficulty="Medium" data-topics="Tree|DFS|Binary Search Tree|Binary Tree">
             <span class="problem-title">Latency Rank Query</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="restored-index-integrity" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="restored-index-integrity" data-difficulty="Medium" data-topics="Tree|DFS|BFS|Binary Search Tree|Binary Tree">
             <span class="problem-title">Restored Index Integrity</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="copper-pad-continuity" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="copper-pad-continuity" data-difficulty="Medium" data-topics="Matrix|DFS|BFS|Union Find">
             <span class="problem-title">Copper Pad Continuity</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sealed-air-pocket-backfill" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="sealed-air-pocket-backfill" data-difficulty="Medium" data-topics="Matrix|DFS|BFS|Union Find">
             <span class="problem-title">Sealed Air Pocket Backfill</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sandbox-topology-replica" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="sandbox-topology-replica" data-difficulty="Medium" data-topics="Hash Table|DFS|BFS|Graph">
             <span class="problem-title">Sandbox Topology Replica</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="lab-unit-converter" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="lab-unit-converter" data-difficulty="Medium" data-topics="Array|String|DFS|BFS|Union Find|Graph">
             <span class="problem-title">Lab Unit Converter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="onboarding-track-feasibility" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="onboarding-track-feasibility" data-difficulty="Medium" data-topics="DFS|BFS|Graph|Topological Sort">
             <span class="problem-title">Onboarding Track Feasibility</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="migration-run-order" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="migration-run-order" data-difficulty="Medium" data-topics="DFS|BFS|Graph|Topological Sort">
             <span class="problem-title">Migration Run Order</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="portal-dice-race" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="portal-dice-race" data-difficulty="Medium" data-topics="Array|BFS|Matrix">
             <span class="problem-title">Portal Dice Race</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="approved-sequence-edits" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="approved-sequence-edits" data-difficulty="Medium" data-topics="Hash Table|String|BFS">
             <span class="problem-title">Approved Sequence Edits</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="hostname-rename-chain" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="hostname-rename-chain" data-difficulty="Hard" data-topics="Hash Table|String|BFS">
             <span class="problem-title">Hostname Rename Chain</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="command-palette-index" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="command-palette-index" data-difficulty="Medium" data-topics="Hash Table|String|Design|Trie">
             <span class="problem-title">Command Palette Index</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="crossword-pattern-matcher" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="crossword-pattern-matcher" data-difficulty="Medium" data-topics="String|DFS|Design|Trie">
             <span class="problem-title">Crossword Pattern Matcher</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="letter-grid-tracer" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="letter-grid-tracer" data-difficulty="Hard" data-topics="Array|String|Backtracking|Trie|Matrix">
             <span class="problem-title">Letter Grid Tracer</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="vanity-dial-expansion" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="vanity-dial-expansion" data-difficulty="Medium" data-topics="Hash Table|String|Backtracking">
             <span class="problem-title">Vanity Dial Expansion</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="canary-host-selection" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="canary-host-selection" data-difficulty="Medium" data-topics="Backtracking">
             <span class="problem-title">Canary Host Selection</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="startup-order-sweep" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="startup-order-sweep" data-difficulty="Medium" data-topics="Array|Backtracking">
             <span class="problem-title">Startup Order Sweep</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="freight-pallet-loadouts" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="freight-pallet-loadouts" data-difficulty="Medium" data-topics="Array|Backtracking">
             <span class="problem-title">Freight Pallet Loadouts</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="interference-free-towers" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="interference-free-towers" data-difficulty="Hard" data-topics="Backtracking">
             <span class="problem-title">Interference Free Towers</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="nesting-fuzzer-corpus" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="nesting-fuzzer-corpus" data-difficulty="Medium" data-topics="String|Dynamic Programming|Backtracking">
             <span class="problem-title">Nesting Fuzzer Corpus</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="letter-panel-tracing" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="letter-panel-tracing" data-difficulty="Medium" data-topics="Array|String|Backtracking|Matrix">
             <span class="problem-title">Letter Panel Tracing</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sensor-calibration-index" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="sensor-calibration-index" data-difficulty="Easy" data-topics="Array|Divide and Conquer|Tree|Binary Search Tree|Binary Tree">
             <span class="problem-title">Sensor Calibration Index</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="maintenance-window-consolidation" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="maintenance-window-consolidation" data-difficulty="Medium" data-topics="Array|Sorting">
             <span class="problem-title">Maintenance Window Consolidation</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="mirrored-tag-segment" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="mirrored-tag-segment" data-difficulty="Medium" data-topics="String|Dynamic Programming|Two Pointers">
             <span class="problem-title">Mirrored Tag Segment</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sorted-schedule-slot" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="sorted-schedule-slot" data-difficulty="Easy" data-topics="Array|Binary Search">
             <span class="problem-title">Sorted Schedule Slot</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="serial-counter-advance" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="serial-counter-advance" data-difficulty="Easy" data-topics="Array|Math">
             <span class="problem-title">Serial Counter Advance</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="wide-register-arithmetic" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="wide-register-arithmetic" data-difficulty="Easy" data-topics="Math|String|Bit Manipulation|Simulation">
             <span class="problem-title">Wide Register Arithmetic</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="unmatched-badge-scan" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="unmatched-badge-scan" data-difficulty="Easy" data-topics="Array|Bit Manipulation">
             <span class="problem-title">Unmatched Badge Scan</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="symmetric-lottery-tickets" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="symmetric-lottery-tickets" data-difficulty="Easy" data-topics="Math">
             <span class="problem-title">Symmetric Lottery Tickets</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="robot-stride-plans" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="robot-stride-plans" data-difficulty="Easy" data-topics="Math|Dynamic Programming|Memoization">
             <span class="problem-title">Robot Stride Plans</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="integer-magnitude-estimator" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="integer-magnitude-estimator" data-difficulty="Easy" data-topics="Math|Binary Search">
             <span class="problem-title">Integer Magnitude Estimator</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="arrangement-count-suffix" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="arrangement-count-suffix" data-difficulty="Medium" data-topics="Math">
             <span class="problem-title">Arrangement Count Suffix</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="highway-billboard-leasing" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="highway-billboard-leasing" data-difficulty="Medium" data-topics="Array|Dynamic Programming">
             <span class="problem-title">Highway Billboard Leasing</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="trading-streak-report" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="trading-streak-report" data-difficulty="Medium" data-topics="Array|Divide and Conquer|Dynamic Programming">
             <span class="problem-title">Trading Streak Report</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="kiosk-token-payout" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="kiosk-token-payout" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Breadth-First Search">
             <span class="problem-title">Kiosk Token Payout</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="benchmark-progress-chain" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="benchmark-progress-chain" data-difficulty="Medium" data-topics="Array|Binary Search|Dynamic Programming">
             <span class="problem-title">Benchmark Progress Chain</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="paged-catalog-lookup" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="paged-catalog-lookup" data-difficulty="Medium" data-topics="Array|Binary Search|Matrix">
             <span class="problem-title">Paged Catalog Lookup</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="signal-crest-locator" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="signal-crest-locator" data-difficulty="Medium" data-topics="Array|Binary Search">
             <span class="problem-title">Signal Crest Locator</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shifted-price-snapshot" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="shifted-price-snapshot" data-difficulty="Medium" data-topics="Array|Binary Search">
             <span class="problem-title">Shifted Price Snapshot</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="conveyor-grid-routing" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="conveyor-grid-routing" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Matrix">
             <span class="problem-title">Conveyor Grid Routing</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="picking-robot-floor-plan" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="picking-robot-floor-plan" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Matrix">
             <span class="problem-title">Picking Robot Floor Plan</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="hashtag-vocabulary-splitter" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="hashtag-vocabulary-splitter" data-difficulty="Medium" data-topics="Array|Hash Table|String|Dynamic Programming|Trie|Memoization">
             <span class="problem-title">Hashtag Vocabulary Splitter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="permission-flag-counter" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="permission-flag-counter" data-difficulty="Easy" data-topics="Divide and Conquer|Bit Manipulation">
             <span class="problem-title">Permission Flag Counter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="replica-write-audit" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="replica-write-audit" data-difficulty="Medium" data-topics="Array|Bit Manipulation">
             <span class="problem-title">Replica Write Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="address-block-shared-bits" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="address-block-shared-bits" data-difficulty="Medium" data-topics="Bit Manipulation">
             <span class="problem-title">Address Block Shared Bits</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="mine-level-descent" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="mine-level-descent" data-difficulty="Medium" data-topics="Array|Dynamic Programming">
             <span class="problem-title">Mine Level Descent</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="scanner-code-reconciliation" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="scanner-code-reconciliation" data-difficulty="Medium" data-topics="String|Dynamic Programming">
             <span class="problem-title">Scanner Code Reconciliation</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="rooftop-panel-footprint" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="rooftop-panel-footprint" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Matrix">
             <span class="problem-title">Rooftop Panel Footprint</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="orbital-energy-window" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="orbital-energy-window" data-difficulty="Medium" data-topics="Array|Divide and Conquer|Dynamic Programming|Queue|Monotonic Queue">
             <span class="problem-title">Orbital Energy Window</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="ring-buffer-dump-lookup" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="ring-buffer-dump-lookup" data-difficulty="Medium" data-topics="Array|Binary Search">
             <span class="problem-title">Ring Buffer Dump Lookup</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="rating-leaderboard-cutoff" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="rating-leaderboard-cutoff" data-difficulty="Medium" data-topics="Array|Divide and Conquer|Sorting|Heap|Quickselect">
             <span class="problem-title">Rating Leaderboard Cutoff</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="log-timestamp-span" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="log-timestamp-span" data-difficulty="Medium" data-topics="Array|Binary Search">
             <span class="problem-title">Log Timestamp Span</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="compound-growth-factor" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="compound-growth-factor" data-difficulty="Medium" data-topics="Math|Recursion">
             <span class="problem-title">Compound Growth Factor</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shared-buffer-keystroke-audit" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="shared-buffer-keystroke-audit" data-difficulty="Medium" data-topics="String|Dynamic Programming">
             <span class="problem-title">Shared Buffer Keystroke Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="spot-capacity-round-trips" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="spot-capacity-round-trips" data-difficulty="Hard" data-topics="Array|Dynamic Programming">
             <span class="problem-title">Spot Capacity Round Trips</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="freight-slot-trading-limit" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="freight-slot-trading-limit" data-difficulty="Hard" data-topics="Array|Dynamic Programming">
             <span class="problem-title">Freight Slot Trading Limit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="firmware-event-chain-ordering" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="firmware-event-chain-ordering" data-difficulty="Medium" data-topics="Linked List|Two Pointers|Divide and Conquer|Sorting|Merge Sort">
             <span class="problem-title">Firmware Event Chain Ordering</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="twin-sensor-midpoint-reading" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="twin-sensor-midpoint-reading" data-difficulty="Hard" data-topics="Array|Binary Search|Divide and Conquer">
             <span class="problem-title">Twin Sensor Midpoint Reading</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="survey-stake-alignment" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="survey-stake-alignment" data-difficulty="Hard" data-topics="Array|Hash Table|Math|Geometry">
             <span class="problem-title">Survey Stake Alignment</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="serial-link-word-mirror" data-difficulty="Easy">
+          <button class="problem-card" type="button" data-problem="serial-link-word-mirror" data-difficulty="Easy" data-topics="Divide and Conquer|Bit Manipulation">
             <span class="problem-title">Serial Link Word Mirror</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="studio-contract-bankroll" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="studio-contract-bankroll" data-difficulty="Hard" data-topics="Array|Greedy|Sorting|Heap">
             <span class="problem-title">Studio Contract Bankroll</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="flight-combo-fare-shortlist" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="flight-combo-fare-shortlist" data-difficulty="Medium" data-topics="Array|Heap|Priority Queue">
             <span class="problem-title">Flight Combo Fare Shortlist</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shard-result-consolidation" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="shard-result-consolidation" data-difficulty="Hard" data-topics="Linked List|Divide and Conquer|Heap|Merge Sort">
             <span class="problem-title">Shard Result Consolidation</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="live-clock-offset-monitor" data-difficulty="Hard">
+          <button class="problem-card" type="button" data-problem="live-clock-offset-monitor" data-difficulty="Hard" data-topics="Two Pointers|Design|Sorting|Heap|Data Stream">
             <span class="problem-title">Live Clock Offset Monitor</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="terrain-mask-tiling" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="terrain-mask-tiling" data-difficulty="Medium" data-topics="Array|Divide and Conquer|Matrix">
             <span class="problem-title">Terrain Mask Tiling</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="bounded-event-queue" data-difficulty="Medium">
+          <button class="problem-card" type="button" data-problem="bounded-event-queue" data-difficulty="Medium" data-topics="Array|Design">
             <span class="problem-title">Bounded Event Queue</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
diff --git a/web/practice-insights.js b/web/practice-insights.js
new file mode 100644
index 00000000..6bc0a9f4
--- /dev/null
+++ b/web/practice-insights.js
@@ -0,0 +1,16 @@
+export function availableTopics(problems) {
+  return [...new Set(problems.flatMap((problem) => problem.topics ?? []))].sort(
+    (left, right) => left.localeCompare(right),
+  );
+}
+
+export function filterProblems(
+  problems,
+  { difficulties = new Set(), topic = "" } = {},
+) {
+  return problems.filter(
+    (problem) =>
+      (!difficulties.size || difficulties.has(problem.difficulty)) &&
+      (!topic || problem.topics.includes(topic)),
+  );
+}
diff --git a/web/styles.css b/web/styles.css
index 5e6af1e9..5d831733 100644
--- a/web/styles.css
+++ b/web/styles.css
@@ -49,7 +49,13 @@ body {
   margin: 0;
   background: var(--page);
   color: var(--ink);
-  font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
+  font-family:
+    ui-sans-serif,
+    system-ui,
+    -apple-system,
+    BlinkMacSystemFont,
+    "Segoe UI",
+    sans-serif;
 }
 
 button {
@@ -227,6 +233,40 @@ p {
   margin: 0.5rem 0;
 }
 
+.practice-filters {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 0.5rem;
+  margin-top: 1rem;
+  padding: 0;
+  border: 0;
+}
+
+.practice-filters legend {
+  width: 100%;
+  color: var(--sub);
+  font-weight: 700;
+}
+
+.practice-filters select,
+.practice-filters button {
+  min-height: 2.5rem;
+}
+
+.practice-filters select {
+  padding: 0.4rem 0.6rem;
+  border: 1px solid var(--hairline);
+  border-radius: 6px;
+  background: var(--surface);
+  color: var(--ink);
+}
+
+.practice-filters p {
+  width: 100%;
+  margin: 0;
+}
+
 .interview-kicker {
   margin-bottom: 0.5rem;
   color: var(--sub);

From 09b749f7c877adc257efa0029b103f2b7ec18fe2 Mon Sep 17 00:00:00 2001
From: daniel_huang <159147443+Danielncku@users.noreply.github.com>
Date: Thu, 1 Oct 2026 22:00:27 +0800
Subject: [PATCH 2/3] Summarize recent practice results

Show a compact snapshot for the latest assessed interviews with pass
rate, current streak, and topics that have more misses than passes. Hide
the snapshot when history is unavailable and cover both success and
failure paths.
---
 tests/browser/lobby.test.js             | 50 +++++++++++++++++++++++++
 tests/browser/practice-insights.test.js | 40 ++++++++++++++++++++
 web/app.js                              | 37 +++++++++++++++++-
 web/index.html                          | 11 ++++++
 web/practice-insights.js                | 50 +++++++++++++++++++++++++
 web/styles.css                          | 17 +++++++++
 6 files changed, 204 insertions(+), 1 deletion(-)

diff --git a/tests/browser/lobby.test.js b/tests/browser/lobby.test.js
index 8d4a7b79..b55c3418 100644
--- a/tests/browser/lobby.test.js
+++ b/tests/browser/lobby.test.js
@@ -393,6 +393,56 @@ lobbyTest(
   },
 );
 
+lobbyTest(
+  "recent assessed reports produce a practice snapshot",
+  async (page) => {
+    reports = [
+      {
+        problemId: EASY[0],
+        createdAt: 30,
+        payload: { report: { decision: "NO_HIRE" } },
+      },
+      {
+        problemId: EASY[1],
+        createdAt: 20,
+        payload: { report: { decision: "HIRE" } },
+      },
+      {
+        problemId: MEDIUM[0],
+        createdAt: 10,
+        payload: { report: { decision: "NO_HIRE" } },
+      },
+    ];
+    await lobby(page);
+
+    assert.equal(
+      await page.locator("#recent-performance-summary").textContent(),
+      "Last 3 assessed interviews: 1 passed, 2 missed (33%).",
+    );
+    assert.equal(await page.locator("#recent-performance").isHidden(), false);
+  },
+);
+
+lobbyTest(
+  "a failed report load hides the recent practice snapshot",
+  async (page) => {
+    failing = new Set(["/api/reports"]);
+    await page.goto(`${base}/`, { waitUntil: "domcontentloaded" });
+    await settles(
+      page,
+      () =>
+        document.querySelector("#progress-summary").textContent ===
+        "Could not load saved account progress.",
+    );
+
+    assert.equal(await page.locator("#recent-performance").isHidden(), true);
+    assert.equal(
+      await page.locator("#recent-performance-summary").textContent(),
+      "",
+    );
+  },
+);
+
 lobbyTest(
   "a candidate who touches nothing gets the server's own default length",
   async (page) => {
diff --git a/tests/browser/practice-insights.test.js b/tests/browser/practice-insights.test.js
index b0b969fc..bed02d50 100644
--- a/tests/browser/practice-insights.test.js
+++ b/tests/browser/practice-insights.test.js
@@ -4,6 +4,7 @@ import assert from "node:assert/strict";
 import {
   availableTopics,
   filterProblems,
+  recentPerformance,
 } from "../../web/practice-insights.js";
 
 const problems = [
@@ -30,3 +31,42 @@ test("difficulty and topic filters combine", () => {
     ["b"],
   );
 });
+
+test("recent performance summarizes assessed reports newest first", () => {
+  const reports = [
+    { problemId: "a", at: 10, report: { decision: "NO_HIRE" } },
+    { problemId: "b", at: 30, report: { decision: "HIRE" } },
+    { problemId: "a", at: 20, report: { decision: "NO_HIRE" } },
+    { problemId: "c", at: 40, report: { decision: "HIRE" } },
+  ];
+
+  assert.deepEqual(recentPerformance(problems, reports, 3), {
+    attempts: 3,
+    passes: 2,
+    misses: 1,
+    passRate: 67,
+    streak: 2,
+    latestDecision: "HIRE",
+    weakTopics: ["Hash Table"],
+  });
+});
+
+test("recent performance ignores unscored and undated entries", () => {
+  assert.equal(
+    recentPerformance(problems, [
+      { problemId: "a", at: null, report: { decision: "NO_HIRE" } },
+      { problemId: "b", at: 20, report: { decision: "PENDING" } },
+    ]),
+    null,
+  );
+});
+
+test("topics with more misses than passes are highlighted", () => {
+  const snapshot = recentPerformance(problems, [
+    { problemId: "a", at: 30, report: { decision: "NO_HIRE" } },
+    { problemId: "a", at: 20, report: { decision: "NO_HIRE" } },
+    { problemId: "b", at: 10, report: { decision: "HIRE" } },
+  ]);
+
+  assert.deepEqual(snapshot.weakTopics, ["Hash Table", "Array"]);
+});
diff --git a/web/app.js b/web/app.js
index ce1f9ae1..808f14ec 100644
--- a/web/app.js
+++ b/web/app.js
@@ -19,7 +19,11 @@ import {
 import { reportMarkdown, reportMarkup } from "./render.js";
 import { downloadMarkdown, reportFilename } from "./download.js";
 import { loadPageMap } from "./problem-data.js";
-import { availableTopics, filterProblems } from "./practice-insights.js";
+import {
+  availableTopics,
+  filterProblems,
+  recentPerformance,
+} from "./practice-insights.js";
 import {
   parseGroundingFile,
   retainedSelection,
@@ -108,6 +112,11 @@ const nodes = {
   problemTopic: document.querySelector("#problem-topic"),
   problemFiltersReset: document.querySelector("#problem-filters-reset"),
   problemFilterSummary: document.querySelector("#problem-filter-summary"),
+  recentPerformance: document.querySelector("#recent-performance"),
+  recentPerformanceSummary: document.querySelector(
+    "#recent-performance-summary",
+  ),
+  recentWeakTopics: document.querySelector("#recent-weak-topics"),
 };
 
 // Every card carries the pressed state from the start, not only the one that
@@ -1127,6 +1136,7 @@ function showProgressError(message) {
   reports = [];
   progressNormalized = [];
   renderPracticeFocus();
+  hideRecentPerformance();
   nodes.historyHeader.hidden = false;
   nodes.history.hidden = false;
   nodes.progressSummary.textContent = message;
@@ -1138,6 +1148,7 @@ function showProgressError(message) {
 
 function showProgress(entries, suffix) {
   renderPracticeFocus();
+  renderRecentPerformance();
   // Normalized once here, not per render: the filters below only select from
   // these rows, so a dropdown change has nothing to re-sanitize.
   progressNormalized = normalizeProgressEntries(entries);
@@ -1160,6 +1171,30 @@ function showProgress(entries, suffix) {
   renderProgress();
 }
 
+function hideRecentPerformance() {
+  nodes.recentPerformance.hidden = true;
+  nodes.recentPerformanceSummary.textContent = "";
+  nodes.recentWeakTopics.textContent = "";
+}
+
+function renderRecentPerformance() {
+  const snapshot = recentPerformance(cards, reports);
+  if (!snapshot) {
+    hideRecentPerformance();
+    return;
+  }
+  const result = `${snapshot.passes} passed, ${snapshot.misses} missed`;
+  const streak =
+    snapshot.streak > 1
+      ? ` Current ${snapshot.latestDecision === "HIRE" ? "pass" : "miss"} streak: ${snapshot.streak}.`
+      : "";
+  nodes.recentPerformanceSummary.textContent = `Last ${snapshot.attempts} assessed interview${snapshot.attempts === 1 ? "" : "s"}: ${result} (${snapshot.passRate}%).${streak}`;
+  nodes.recentWeakTopics.textContent = snapshot.weakTopics.length
+    ? `Topics to revisit: ${snapshot.weakTopics.slice(0, 5).join(", ")}.`
+    : "No recurring weak topic in these interviews.";
+  nodes.recentPerformance.hidden = false;
+}
+
 /// `attempts` is what `progressModelFrom` already filtered, oldest first.
 ///
 /// Taken rather than re-derived: normalizing again here is what let the trends
diff --git a/web/index.html b/web/index.html
index e6782c74..725c9ba5 100644
--- a/web/index.html
+++ b/web/index.html
@@ -962,6 +962,17 @@ <h1>Practice a live technical interview</h1>
         </button>
       </section>
 
+      <section
+        id="recent-performance"
+        class="recent-performance"
+        aria-labelledby="recent-performance-title"
+        hidden
+      >
+        <h2 id="recent-performance-title">Recent practice snapshot</h2>
+        <p id="recent-performance-summary" aria-live="polite"></p>
+        <p id="recent-weak-topics" class="muted small"></p>
+      </section>
+
       <div id="history-header" class="history-header" hidden>
         <h2 id="progress-title">Interview progress</h2>
         <button
diff --git a/web/practice-insights.js b/web/practice-insights.js
index 6bc0a9f4..177a3c1f 100644
--- a/web/practice-insights.js
+++ b/web/practice-insights.js
@@ -14,3 +14,53 @@ export function filterProblems(
       (!topic || problem.topics.includes(topic)),
   );
 }
+
+const ASSESSED = new Set(["HIRE", "NO_HIRE"]);
+
+export function recentPerformance(problems, reports, limit = 8) {
+  const topicsByProblem = new Map(
+    problems.map((problem) => [problem.id, problem.topics ?? []]),
+  );
+  const attempts = reports
+    .filter(
+      (entry) =>
+        Number.isFinite(entry.at) && ASSESSED.has(entry.report?.decision),
+    )
+    .sort((left, right) => right.at - left.at)
+    .slice(0, limit);
+  if (!attempts.length) return null;
+
+  const passes = attempts.filter(
+    (entry) => entry.report.decision === "HIRE",
+  ).length;
+  const topicResults = new Map();
+  for (const entry of attempts) {
+    for (const topic of topicsByProblem.get(entry.problemId) ?? []) {
+      const result = topicResults.get(topic) ?? { passes: 0, misses: 0 };
+      result[entry.report.decision === "HIRE" ? "passes" : "misses"] += 1;
+      topicResults.set(topic, result);
+    }
+  }
+  const weakTopics = [...topicResults]
+    .filter(([, result]) => result.misses > result.passes)
+    .sort(
+      ([leftTopic, left], [rightTopic, right]) =>
+        right.misses - right.passes - (left.misses - left.passes) ||
+        leftTopic.localeCompare(rightTopic),
+    )
+    .map(([topic]) => topic);
+  const latestDecision = attempts[0].report.decision;
+  const streak = attempts.findIndex(
+    (entry) => entry.report.decision !== latestDecision,
+  );
+
+  return {
+    attempts: attempts.length,
+    passes,
+    misses: attempts.length - passes,
+    passRate: Math.round((passes / attempts.length) * 100),
+    streak: streak === -1 ? attempts.length : streak,
+    latestDecision,
+    weakTopics,
+  };
+}
diff --git a/web/styles.css b/web/styles.css
index 5d831733..02a27a1d 100644
--- a/web/styles.css
+++ b/web/styles.css
@@ -331,6 +331,23 @@ p {
   margin-top: 1rem;
 }
 
+.recent-performance {
+  margin-top: 1.5rem;
+  padding: 1rem;
+  border: 1px solid var(--hairline);
+  border-radius: 8px;
+  background: var(--surface);
+}
+
+.recent-performance h2,
+.recent-performance p {
+  margin: 0;
+}
+
+.recent-performance p + p {
+  margin-top: 0.5rem;
+}
+
 .interview-context {
   margin-top: 1rem;
   padding: 0.75rem;

From 603676f0026d36491ac76a22b9daa8e9f9649580 Mon Sep 17 00:00:00 2001
From: daniel_huang <159147443+Danielncku@users.noreply.github.com>
Date: Fri, 2 Oct 2026 23:55:59 +0800
Subject: [PATCH 3/3] Refine lobby topic filtering

Keep problem topic metadata out of the initial markup and load it only
when the candidate opens the picker. Reset topic selection on restore
and keep manual choices aligned with the combined filters.

Preserve due-review priority across topic filters, exclude incomplete
reports from recent performance, and add regression coverage for the
reviewed cases.
---
 scripts/gen-problem-cards.py            |  43 +-
 tests/browser/dom.js                    |   3 +-
 tests/browser/lobby-render.test.js      |  10 +-
 tests/browser/lobby.test.js             | 131 +++-
 tests/browser/practice-insights.test.js |  42 +-
 tests/browser/problem-picker.test.js    |  16 +
 web/app.js                              |  73 ++-
 web/index.html                          | 304 +++++-----
 web/practice-insights.js                |  11 +-
 web/problem-data.js                     |  12 +
 web/problem-picker.js                   |   5 +-
 web/problem-topics.json                 | 755 ++++++++++++++++++++++++
 12 files changed, 1178 insertions(+), 227 deletions(-)
 create mode 100644 web/problem-topics.json

diff --git a/scripts/gen-problem-cards.py b/scripts/gen-problem-cards.py
index 14b23b39..59fbe110 100644
--- a/scripts/gen-problem-cards.py
+++ b/scripts/gen-problem-cards.py
@@ -19,6 +19,7 @@
 # the only one that reads them. Run it first.
 PAGE_MAP = ROOT / "web" / "problem-pages.json"
 INDEX = ROOT / "web" / "index.html"
+TOPIC_MAP = ROOT / "web" / "problem-topics.json"
 # Matched without their indentation, which the surrounding markup owns and has
 # already changed once: wrapping the grid in a `<details>` moved it two columns
 # right, and the six-space literals these used to be went on matching only
@@ -43,18 +44,15 @@ def read_json(path: Path) -> object:
 def card(problem: dict[str, object], page: str, title: str) -> str:
     """One lobby card, named the way the interview will name the exercise.
 
-    Keyed by page name, with the scenario title and topic metadata: the
-    recommendation line reads the title off this card, and "Recommended: Coin
-    Change", a `coin-change` key or a "Dynamic Programming" tag tells the
-    candidate what they are about to be asked. Topics stay in data attributes
-    for local filtering and are not rendered on the card. The published title
-    is not in the page at all; the source slot is filled from the page map only
-    when the candidate turns that on to drill one problem by name.
+    Keyed by page name, with the scenario title the recommendation line reads.
+    A `coin-change` key, published title or "Dynamic Programming" tag tells the
+    candidate what they are about to be asked, so none ships in the initial
+    page. The published title and topic map are fetched only after the candidate
+    opts into the corresponding picker control.
     """
-    topics = "|".join(str(topic) for topic in problem.get("topics", []))
     return "\n".join(
         [
-            f'  <button class="problem-card" type="button" data-problem="{html.escape(page)}" data-difficulty="{html.escape(problem["difficulty"])}" data-topics="{html.escape(topics)}">',
+            f'  <button class="problem-card" type="button" data-problem="{html.escape(page)}" data-difficulty="{html.escape(problem["difficulty"])}">',
             f'    <span class="problem-title">{html.escape(title)}</span>',
             '    <span class="problem-source" hidden></span>',
             f'    <span class="problem-meta">{html.escape(problem["difficulty"])}</span>',
@@ -63,8 +61,7 @@ def card(problem: dict[str, object], page: str, title: str) -> str:
     )
 
 
-def generated(problems: list) -> str:
-    pages = read_json(PAGE_MAP)
+def generated(problems: list, pages: dict) -> str:
     cards = "\n".join(
         card(problem, pages[problem["id"]]["page"], pages[problem["id"]]["title"])
         for problem in problems
@@ -79,6 +76,15 @@ def generated(problems: list) -> str:
     )
 
 
+def generated_topics(problems: list, pages: dict) -> str:
+    """The opt-in topic filter's page-to-topic lookup."""
+    mapping = {
+        pages[problem["id"]]["page"]: problem.get("topics", [])
+        for problem in problems
+    }
+    return json.dumps(mapping, ensure_ascii=False, indent=2) + "\n"
+
+
 def main() -> int:
     args = parse_args()
     html_text = INDEX.read_text(encoding="utf-8")
@@ -103,12 +109,20 @@ def main() -> int:
         return 1
 
     problems = read_json(SOURCE)
-    block = textwrap.indent(generated(problems), indent)
+    pages = read_json(PAGE_MAP)
+    block = textwrap.indent(generated(problems, pages), indent)
     updated = html_text[: opening.start()] + block + html_text[end.end() :]
+    topics = generated_topics(problems, pages)
+    current_topics = TOPIC_MAP.read_text(encoding="utf-8") if TOPIC_MAP.exists() else ""
     if args.check:
+        stale = []
         if updated != html_text:
+            stale.append("web/index.html problem cards")
+        if topics != current_topics:
+            stale.append("web/problem-topics.json")
+        if stale:
             print(
-                "web/index.html problem cards are stale; run: python3 scripts/gen-problem-cards.py",
+                f"{', '.join(stale)} are stale; run: python3 scripts/gen-problem-cards.py",
                 file=sys.stderr,
             )
             return 1
@@ -117,6 +131,9 @@ def main() -> int:
     if updated != html_text:
         INDEX.write_text(updated, encoding="utf-8")
         print(f"updated {len(problems)} problem cards in web/index.html")
+    if topics != current_topics:
+        TOPIC_MAP.write_text(topics, encoding="utf-8")
+        print(f"updated {len(problems)} problem topics in web/problem-topics.json")
     return 0
 
 
diff --git a/tests/browser/dom.js b/tests/browser/dom.js
index fa0558b8..c875e7d2 100644
--- a/tests/browser/dom.js
+++ b/tests/browser/dom.js
@@ -61,6 +61,7 @@ register("./dom-hooks.js", pathToFileURL(`${import.meta.dirname}/`));
 /// properties that put a string on the page without going through `textContent`.
 const SPOKEN_ATTRIBUTES = ["title", "ariaLabel", "alt", "placeholder", "value"];
 const MARKUP = ["innerHTML", "innerText", "outerHTML"];
+const FORM_CONTROLS = new Set(["button", "input", "select", "textarea"]);
 
 class Element {
   #text = "";
@@ -344,7 +345,7 @@ export function installDocument(markup) {
           created.dataset[key] = value;
         }
       }
-      if ("value" in element.attributes)
+      if (FORM_CONTROLS.has(element.tag) && "value" in element.attributes)
         created.value = element.attributes.value;
       nodes.set(element, created);
     }
diff --git a/tests/browser/lobby-render.test.js b/tests/browser/lobby-render.test.js
index c926cb47..db2d7b1b 100644
--- a/tests/browser/lobby-render.test.js
+++ b/tests/browser/lobby-render.test.js
@@ -46,8 +46,6 @@ const SIGNED_OUT = {
   start: "Start interview",
   "progress-summary": "Could not load progress saved on this device.",
 };
-const PROBLEM_FILTERS = new Set(["problem-topic", "problem-filter-summary"]);
-
 test("the lobby page loads outside a browser and says what it was given", () => {
   for (const [id, expected] of Object.entries(SIGNED_OUT)) {
     assert.deepEqual(dom.node(id).spoken(), [expected], `#${id}`);
@@ -63,13 +61,7 @@ test("no other panel of the lobby speaks before anything has loaded", () => {
   const spoke = [];
   for (const [, id] of markup.matchAll(/id="([^"]+)"/g)) {
     const node = dom.node(id);
-    if (
-      node &&
-      node.spoken().length &&
-      !(id in SIGNED_OUT) &&
-      !PROBLEM_FILTERS.has(id)
-    )
-      spoke.push(id);
+    if (node && node.spoken().length && !(id in SIGNED_OUT)) spoke.push(id);
   }
   assert.deepEqual(
     spoke,
diff --git a/tests/browser/lobby.test.js b/tests/browser/lobby.test.js
index b55c3418..2449a798 100644
--- a/tests/browser/lobby.test.js
+++ b/tests/browser/lobby.test.js
@@ -221,6 +221,7 @@ const markupDuration = () =>
 /// The page name a card ships in the URL, from the map the generator writes.
 const pageOf = (problemId) =>
   JSON.parse(read("web/problem-pages.json"))[problemId].page;
+const TOPICS_BY_PAGE = JSON.parse(read("web/problem-topics.json"));
 
 const hired = (problemId) => ({
   problemId,
@@ -331,6 +332,13 @@ const restore = (page) =>
     ),
   );
 
+async function openTopicFilter(page) {
+  await page.click("details.problem-picker summary");
+  await page.waitForFunction(
+    () => !document.querySelector("#problem-topic").disabled,
+  );
+}
+
 /// What the difficulty filter did to one card.
 const cardInfo = (page, id) =>
   page.evaluate((problem) => {
@@ -365,22 +373,44 @@ lobbyTest(
 lobbyTest(
   "topic and difficulty filters narrow the problem cards together",
   async (page) => {
+    const requests = [];
+    page.on("request", (request) =>
+      requests.push(new URL(request.url()).pathname),
+    );
     await lobby(page);
-    await page.click("details.problem-picker summary");
+    assert.equal(
+      requests.includes("/problem-topics.json"),
+      false,
+      "the initial lobby disclosed the topic map",
+    );
+    assert.equal(
+      await page.locator("[data-topics]").count(),
+      0,
+      "a problem card disclosed its topics in the HTML",
+    );
+    assert.equal(
+      await page.locator("#problem-filter-summary").textContent(),
+      "",
+      "the untouched live region announced a count",
+    );
+    await openTopicFilter(page);
+    assert.equal(requests.includes("/problem-topics.json"), true);
 
     await page.selectOption("#problem-topic", "Array");
     const filtered = await page
       .locator("[data-problem]:visible")
       .evaluateAll((cards) =>
         cards.map((card) => ({
+          id: card.dataset.problem,
           difficulty: card.dataset.difficulty,
-          topics: card.dataset.topics.split("|"),
         })),
       );
     assert.ok(filtered.length > 0, "the topic filter hid every problem");
     assert.ok(
       filtered.every(
-        (card) => card.difficulty === "Medium" && card.topics.includes("Array"),
+        (card) =>
+          card.difficulty === "Medium" &&
+          TOPICS_BY_PAGE[card.id].includes("Array"),
       ),
       "a visible card did not match both filters",
     );
@@ -390,6 +420,96 @@ lobbyTest(
       (await page.locator("[data-problem]:visible").count()) > filtered.length,
       "reset did not restore the other Medium problems",
     );
+    assert.equal(
+      await page.locator("#problem-filter-summary").textContent(),
+      "",
+    );
+  },
+);
+
+lobbyTest("a topic choice does not survive a lobby restore", async (page) => {
+  await lobby(page);
+  await openTopicFilter(page);
+  await page.selectOption("#problem-topic", "Array");
+  assert.match(
+    await page.locator("#problem-filter-summary").textContent(),
+    /tagged Array/,
+  );
+
+  await restore(page);
+  await awaitReady(page);
+  assert.equal(await page.locator("#problem-topic").inputValue(), "");
+  assert.equal(await page.locator("#problem-filter-summary").textContent(), "");
+});
+
+lobbyTest(
+  "a hidden manual pick does not survive the combined filters",
+  async (page) => {
+    const hardArray = Object.entries(TOPICS_BY_PAGE).find(
+      ([pageName, topics]) =>
+        topics.includes("Array") &&
+        read("web/index.html").includes(
+          `data-problem="${pageName}" data-difficulty="Hard"`,
+        ),
+    )[0];
+    await lobby(page);
+    await openTopicFilter(page);
+    await page.evaluate((id) => {
+      const card = document.querySelector(`[data-problem="${id}"]`);
+      card.hidden = false;
+      card.click();
+    }, hardArray);
+
+    await page.selectOption("#problem-topic", "Array");
+    const state = await snapshot(page);
+    assert.notEqual(state.card, hardArray);
+    assert.equal((await cardInfo(page, hardArray)).hidden, true);
+    assert.equal((await cardInfo(page, state.card)).hidden, false);
+  },
+);
+
+lobbyTest(
+  "a due review outside the selected topic remains the first priority",
+  async (page) => {
+    const due = pageOf("valid-parentheses");
+    assert.equal(TOPICS_BY_PAGE[due].includes("Array"), false);
+    reports = [savedAttempt(due)];
+    await lobby(page);
+    await openTopicFilter(page);
+    await page.selectOption("#problem-topic", "Array");
+
+    const state = await snapshot(page);
+    assert.equal(state.card, due);
+    assert.match(state.note, /Review due after/);
+    assert.equal((await cardInfo(page, due)).hidden, false);
+  },
+);
+
+lobbyTest(
+  "a completed topic and level are described without overstating progress",
+  async (page) => {
+    const markup = read("web/index.html");
+    const mediumArray = Object.entries(TOPICS_BY_PAGE)
+      .filter(
+        ([pageName, topics]) =>
+          topics.includes("Array") &&
+          markup.includes(
+            `data-problem="${pageName}" data-difficulty="Medium"`,
+          ),
+      )
+      .map(([pageName]) => pageName);
+    reports = mediumArray.map(hired);
+    await lobby(page);
+    await setLevel(page, "Medium", true);
+    await setLevel(page, "Easy", false);
+    await setLevel(page, "Hard", false);
+    await openTopicFilter(page);
+    await page.selectOption("#problem-topic", "Array");
+
+    assert.match(
+      (await snapshot(page)).note,
+      /You have passed every problem matching this topic and level\./,
+    );
   },
 );
 
@@ -397,6 +517,11 @@ lobbyTest(
   "recent assessed reports produce a practice snapshot",
   async (page) => {
     reports = [
+      {
+        problemId: HARD[0],
+        createdAt: 40,
+        payload: { report: { incomplete: true, decision: "HIRE" } },
+      },
       {
         problemId: EASY[0],
         createdAt: 30,
diff --git a/tests/browser/practice-insights.test.js b/tests/browser/practice-insights.test.js
index bed02d50..b85f63d9 100644
--- a/tests/browser/practice-insights.test.js
+++ b/tests/browser/practice-insights.test.js
@@ -13,6 +13,15 @@ const problems = [
   { id: "c", difficulty: "Hard", topics: ["Graph"] },
 ];
 
+const report = (problemId, at, decision) => ({
+  problemId,
+  at,
+  report: {
+    decision,
+    topics: problems.find((problem) => problem.id === problemId)?.topics ?? [],
+  },
+});
+
 test("topics are unique and sorted", () => {
   assert.deepEqual(availableTopics(problems), [
     "Array",
@@ -34,13 +43,13 @@ test("difficulty and topic filters combine", () => {
 
 test("recent performance summarizes assessed reports newest first", () => {
   const reports = [
-    { problemId: "a", at: 10, report: { decision: "NO_HIRE" } },
-    { problemId: "b", at: 30, report: { decision: "HIRE" } },
-    { problemId: "a", at: 20, report: { decision: "NO_HIRE" } },
-    { problemId: "c", at: 40, report: { decision: "HIRE" } },
+    report("a", 10, "NO_HIRE"),
+    report("b", 30, "HIRE"),
+    report("a", 20, "NO_HIRE"),
+    report("c", 40, "HIRE"),
   ];
 
-  assert.deepEqual(recentPerformance(problems, reports, 3), {
+  assert.deepEqual(recentPerformance(reports, 3), {
     attempts: 3,
     passes: 2,
     misses: 1,
@@ -53,7 +62,7 @@ test("recent performance summarizes assessed reports newest first", () => {
 
 test("recent performance ignores unscored and undated entries", () => {
   assert.equal(
-    recentPerformance(problems, [
+    recentPerformance([
       { problemId: "a", at: null, report: { decision: "NO_HIRE" } },
       { problemId: "b", at: 20, report: { decision: "PENDING" } },
     ]),
@@ -61,11 +70,24 @@ test("recent performance ignores unscored and undated entries", () => {
   );
 });
 
+test("recent performance ignores incomplete reports with a decision", () => {
+  assert.equal(
+    recentPerformance([
+      {
+        problemId: "a",
+        at: 20,
+        report: { incomplete: true, decision: "HIRE", topics: ["Array"] },
+      },
+    ]),
+    null,
+  );
+});
+
 test("topics with more misses than passes are highlighted", () => {
-  const snapshot = recentPerformance(problems, [
-    { problemId: "a", at: 30, report: { decision: "NO_HIRE" } },
-    { problemId: "a", at: 20, report: { decision: "NO_HIRE" } },
-    { problemId: "b", at: 10, report: { decision: "HIRE" } },
+  const snapshot = recentPerformance([
+    report("a", 30, "NO_HIRE"),
+    report("a", 20, "NO_HIRE"),
+    report("b", 10, "HIRE"),
   ]);
 
   assert.deepEqual(snapshot.weakTopics, ["Hash Table", "Array"]);
diff --git a/tests/browser/problem-picker.test.js b/tests/browser/problem-picker.test.js
index 64d8fee3..7cbdebb5 100644
--- a/tests/browser/problem-picker.test.js
+++ b/tests/browser/problem-picker.test.js
@@ -145,6 +145,22 @@ test("a due review at a level the lobby moved past is still recommended", () =>
   assert.equal(choice.review.intervalDays, 1);
 });
 
+test("a due review outside an opt-in filter stays the first priority", () => {
+  const now = 10 * day;
+  const filtered = bank.filter((problem) => problem.id !== "passed");
+  const choice = pickProblem(
+    filtered,
+    new Set(["Easy"]),
+    [completed("passed", now - day)],
+    first,
+    now,
+    undefined,
+    bank,
+  );
+  assert.equal(choice.picked.id, "passed");
+  assert.equal(choice.review.intervalDays, 1);
+});
+
 test("a failed review resets the interval", () => {
   const now = 10 * day;
   const choice = pickProblem(
diff --git a/web/app.js b/web/app.js
index 808f14ec..1ee83e6c 100644
--- a/web/app.js
+++ b/web/app.js
@@ -18,7 +18,7 @@ import {
 } from "./progress.js";
 import { reportMarkdown, reportMarkup } from "./render.js";
 import { downloadMarkdown, reportFilename } from "./download.js";
-import { loadPageMap } from "./problem-data.js";
+import { loadPageMap, loadTopicMap } from "./problem-data.js";
 import {
   availableTopics,
   filterProblems,
@@ -110,6 +110,7 @@ const nodes = {
   groundingError: document.querySelector("#grounding-error"),
   durationNote: document.querySelector("#duration-note"),
   problemTopic: document.querySelector("#problem-topic"),
+  problemPicker: document.querySelector("details.problem-picker"),
   problemFiltersReset: document.querySelector("#problem-filters-reset"),
   problemFilterSummary: document.querySelector("#problem-filter-summary"),
   recentPerformance: document.querySelector("#recent-performance"),
@@ -126,9 +127,7 @@ const cards = [...document.querySelectorAll("[data-problem]")].map(
   (button) => ({
     id: button.dataset.problem,
     difficulty: button.dataset.difficulty,
-    topics: String(button.dataset.topics || "")
-      .split("|")
-      .filter(Boolean),
+    topics: [],
     button,
   }),
 );
@@ -175,21 +174,37 @@ showSources.addEventListener("change", () => {
 });
 void applySources();
 const levels = [...document.querySelectorAll('[name="difficulty"]')];
-const TOPIC_KEY = "codetrial.problemTopic";
-const topics = availableTopics(cards);
-for (const topic of topics) {
-  const option = document.createElement("option");
-  option.value = topic;
-  option.textContent = topic;
-  nodes.problemTopic.append(option);
-}
-try {
-  const storedTopic = localStorage.getItem(TOPIC_KEY) ?? "";
-  if (topics.includes(storedTopic)) nodes.problemTopic.value = storedTopic;
-} catch {
-  /* the filter still works for this visit */
+let topicLoad;
+nodes.problemTopic.disabled = true;
+
+// A topic names the technique behind a scenario, so the page does not ship the
+// full lookup. Opening the specific-problem picker opts into fetching it; no
+// later visit inherits that choice.
+async function loadTopics() {
+  topicLoad ??= loadTopicMap()
+    .then((mapping) => {
+      for (const card of cards) card.topics = mapping?.[card.id] ?? [];
+      for (const topic of availableTopics(cards)) {
+        const option = document.createElement("option");
+        option.value = topic;
+        option.textContent = topic;
+        nodes.problemTopic.append(option);
+      }
+      nodes.problemTopic.disabled = false;
+      return true;
+    })
+    .catch(() => {
+      nodes.problemFilterSummary.textContent =
+        "Topic filters could not be loaded.";
+      return false;
+    });
+  return topicLoad;
 }
 
+nodes.problemPicker.addEventListener("toggle", () => {
+  if (nodes.problemPicker.open) void loadTopics();
+});
+
 // A picked card is a choice about this one interview, not about the filter the
 // checkboxes carry, so it leaves them alone. It suggests a length to go with
 // the level it belongs to, which `setDuration` applies only if the candidate
@@ -244,21 +259,11 @@ for (const input of levels) {
 }
 
 nodes.problemTopic.addEventListener("change", () => {
-  try {
-    localStorage.setItem(TOPIC_KEY, nodes.problemTopic.value);
-  } catch {
-    /* the filter still works for this visit */
-  }
   filterSelectionChanged();
 });
 
 nodes.problemFiltersReset.addEventListener("click", () => {
   nodes.problemTopic.value = "";
-  try {
-    localStorage.removeItem(TOPIC_KEY);
-  } catch {
-    /* the filter still resets for this visit */
-  }
   filterSelectionChanged();
 });
 
@@ -469,6 +474,8 @@ window.addEventListener("pageshow", (event) => {
   // late enough to re-enable a button the candidate already pressed and hand
   // them a second navigation.
   if (!event.persisted) return;
+  nodes.problemTopic.value = "";
+  applyProblemFilters();
   // The cache holds the page as it was before the candidate left, and a login
   // recorded on the way out is in none of it, so restoring what it holds told
   // somebody who had just signed in to sign in. Ask the server instead, and
@@ -936,13 +943,14 @@ function applyProblemFilters(difficulties = selectedDifficulties()) {
   );
   for (const card of cards) card.button.hidden = !visible.has(card);
   const topic = nodes.problemTopic.value;
-  nodes.problemFilterSummary.textContent = `${visible.size} problem${visible.size === 1 ? "" : "s"}${topic ? ` tagged ${topic}` : ""} shown.`;
+  nodes.problemFilterSummary.textContent = topic
+    ? `${visible.size} problem${visible.size === 1 ? "" : "s"} tagged ${topic} shown.`
+    : "";
 }
 
 function filterSelectionChanged() {
-  const eligible = new Set(topicEligibleCards());
   applyProblemFilters();
-  if (manualProblem && eligible.has(problem)) return;
+  if (manualProblem && !problem?.button.hidden) return;
   manualProblem = false;
   roll = Math.random();
   avoidedProblem = undefined;
@@ -967,6 +975,7 @@ function recommend(note = "") {
     () => roll,
     undefined,
     avoidedProblem,
+    cards,
   );
   // Nothing to offer is still an answer, and it has to go through `setProblem`
   // like every other one. Returning here left whatever was picked for the
@@ -990,7 +999,7 @@ function recommend(note = "") {
     return;
   }
   nodes.recommendation.textContent = choice.repeat
-    ? `${note}Selected problem: ${title(choice.picked)}. You have passed every problem at this level.`
+    ? `${note}Selected problem: ${title(choice.picked)}. ${nodes.problemTopic.value ? "You have passed every problem matching this topic and level." : "You have passed every problem at this level."}`
     : `${note}Selected problem: ${title(choice.picked)}.`;
 }
 
@@ -1178,7 +1187,7 @@ function hideRecentPerformance() {
 }
 
 function renderRecentPerformance() {
-  const snapshot = recentPerformance(cards, reports);
+  const snapshot = recentPerformance(reports);
   if (!snapshot) {
     hideRecentPerformance();
     return;
diff --git a/web/index.html b/web/index.html
index 725c9ba5..56b935bd 100644
--- a/web/index.html
+++ b/web/index.html
@@ -80,7 +80,7 @@ <h1>Practice a live technical interview</h1>
         <fieldset class="practice-filters">
           <legend>Filter problems</legend>
           <label for="problem-topic">Topic</label>
-          <select id="problem-topic">
+          <select id="problem-topic" disabled>
             <option value="">All topics</option>
           </select>
           <button id="problem-filters-reset" type="button">Reset filter</button>
@@ -93,757 +93,757 @@ <h1>Practice a live technical interview</h1>
         <!-- prettier-ignore -->
         <section class="problem-grid" aria-label="Problems">
           <!-- Generated by scripts/gen-problem-cards.py from problem-bank/. Do not edit by hand. -->
-          <button class="problem-card" type="button" data-problem="template-delimiter-audit" data-difficulty="Easy" data-topics="String|Stack">
+          <button class="problem-card" type="button" data-problem="template-delimiter-audit" data-difficulty="Easy">
             <span class="problem-title">Template Delimiter Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="chargeback-pair-match" data-difficulty="Easy" data-topics="Array|Hash Table">
+          <button class="problem-card" type="button" data-problem="chargeback-pair-match" data-difficulty="Easy">
             <span class="problem-title">Chargeback Pair Match</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="firmware-buffer-splice" data-difficulty="Easy" data-topics="Array|Two Pointers|Sorting">
+          <button class="problem-card" type="button" data-problem="firmware-buffer-splice" data-difficulty="Easy">
             <span class="problem-title">Firmware Buffer Splice</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="muted-alert-filter" data-difficulty="Easy" data-topics="Array|Two Pointers">
+          <button class="problem-card" type="button" data-problem="muted-alert-filter" data-difficulty="Easy">
             <span class="problem-title">Muted Alert Filter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="telemetry-reading-dedupe" data-difficulty="Easy" data-topics="Array|Two Pointers">
+          <button class="problem-card" type="button" data-problem="telemetry-reading-dedupe" data-difficulty="Easy">
             <span class="problem-title">Telemetry Reading Dedupe</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="alert-digest-trimming" data-difficulty="Medium" data-topics="Array|Two Pointers">
+          <button class="problem-card" type="button" data-problem="alert-digest-trimming" data-difficulty="Medium">
             <span class="problem-title">Alert Digest Trimming</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="replica-quorum-version" data-difficulty="Easy" data-topics="Array|Hash Table|Divide and Conquer|Counting">
+          <button class="problem-card" type="button" data-problem="replica-quorum-version" data-difficulty="Easy">
             <span class="problem-title">Replica Quorum Version</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="carousel-slot-shift" data-difficulty="Medium" data-topics="Array|Math|Two Pointers">
+          <button class="problem-card" type="button" data-problem="carousel-slot-shift" data-difficulty="Medium">
             <span class="problem-title">Carousel Slot Shift</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="single-resale-window" data-difficulty="Easy" data-topics="Array|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="single-resale-window" data-difficulty="Easy">
             <span class="problem-title">Single Resale Window</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="single-slot-reseller" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Greedy">
+          <button class="problem-card" type="button" data-problem="single-slot-reseller" data-difficulty="Medium">
             <span class="problem-title">Single Slot Reseller</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="relay-chain-reachability" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Greedy">
+          <button class="problem-card" type="button" data-problem="relay-chain-reachability" data-difficulty="Medium">
             <span class="problem-title">Relay Chain Reachability</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="drone-pad-hopping" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Greedy">
+          <button class="problem-card" type="button" data-problem="drone-pad-hopping" data-difficulty="Medium">
             <span class="problem-title">Drone Pad Hopping</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="package-impact-score" data-difficulty="Medium" data-topics="Array|Sorting|Counting Sort">
+          <button class="problem-card" type="button" data-problem="package-impact-score" data-difficulty="Medium">
             <span class="problem-title">Package Impact Score</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="backend-pool-sampler" data-difficulty="Medium" data-topics="Array|Hash Table|Math|Design|Randomized">
+          <button class="problem-card" type="button" data-problem="backend-pool-sampler" data-difficulty="Medium">
             <span class="problem-title">Backend Pool Sampler</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="pipeline-stage-gains" data-difficulty="Medium" data-topics="Array|Prefix Sum">
+          <button class="problem-card" type="button" data-problem="pipeline-stage-gains" data-difficulty="Medium">
             <span class="problem-title">Pipeline Stage Gains</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="circular-route-charging" data-difficulty="Medium" data-topics="Array|Greedy">
+          <button class="problem-card" type="button" data-problem="circular-route-charging" data-difficulty="Medium">
             <span class="problem-title">Circular Route Charging</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shift-crew-bonus-points" data-difficulty="Hard" data-topics="Array|Greedy">
+          <button class="problem-card" type="button" data-problem="shift-crew-bonus-points" data-difficulty="Hard">
             <span class="problem-title">Shift Crew Bonus Points</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="terrain-runoff-pooling" data-difficulty="Hard" data-topics="Array|Two Pointers|Dynamic Programming|Stack|Monotonic Stack">
+          <button class="problem-card" type="button" data-problem="terrain-runoff-pooling" data-difficulty="Hard">
             <span class="problem-title">Terrain Runoff Pooling</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="archive-volume-numbers" data-difficulty="Easy" data-topics="Hash Table|Math|String">
+          <button class="problem-card" type="button" data-problem="archive-volume-numbers" data-difficulty="Easy">
             <span class="problem-title">Archive Volume Numbers</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="film-credits-year-stamp" data-difficulty="Medium" data-topics="Hash Table|Math|String">
+          <button class="problem-card" type="button" data-problem="film-credits-year-stamp" data-difficulty="Medium">
             <span class="problem-title">Film Credits Year Stamp</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="autocomplete-token-width" data-difficulty="Easy" data-topics="String">
+          <button class="problem-card" type="button" data-problem="autocomplete-token-width" data-difficulty="Easy">
             <span class="problem-title">Autocomplete Token Width</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="metric-namespace-root" data-difficulty="Easy" data-topics="String|Trie">
+          <button class="problem-card" type="button" data-problem="metric-namespace-root" data-difficulty="Easy">
             <span class="problem-title">Metric Namespace Root</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="backwards-caption-repair" data-difficulty="Medium" data-topics="String|Two Pointers">
+          <button class="problem-card" type="button" data-problem="backwards-caption-repair" data-difficulty="Medium">
             <span class="problem-title">Backwards Caption Repair</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="bouncing-print-head" data-difficulty="Medium" data-topics="String">
+          <button class="problem-card" type="button" data-problem="bouncing-print-head" data-difficulty="Medium">
             <span class="problem-title">Bouncing Print Head</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="firmware-signature-scan" data-difficulty="Easy" data-topics="Two Pointers|String|String Matching">
+          <button class="problem-card" type="button" data-problem="firmware-signature-scan" data-difficulty="Easy">
             <span class="problem-title">Firmware Signature Scan</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="thermal-receipt-layout" data-difficulty="Hard" data-topics="Array|String|Simulation">
+          <button class="problem-card" type="button" data-problem="thermal-receipt-layout" data-difficulty="Hard">
             <span class="problem-title">Thermal Receipt Layout</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="mirror-phrase-contest-filter" data-difficulty="Easy" data-topics="Two Pointers|String">
+          <button class="problem-card" type="button" data-problem="mirror-phrase-contest-filter" data-difficulty="Easy">
             <span class="problem-title">Mirror Phrase Contest Filter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="ordered-event-trace-check" data-difficulty="Easy" data-topics="Two Pointers|String|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="ordered-event-trace-check" data-difficulty="Easy">
             <span class="problem-title">Ordered Event Trace Check</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="billboard-pole-banner" data-difficulty="Medium" data-topics="Array|Two Pointers|Greedy">
+          <button class="problem-card" type="button" data-problem="billboard-pole-banner" data-difficulty="Medium">
             <span class="problem-title">Billboard Pole Banner</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="gift-card-bundle-pair" data-difficulty="Medium" data-topics="Array|Two Pointers|Binary Search">
+          <button class="problem-card" type="button" data-problem="gift-card-bundle-pair" data-difficulty="Medium">
             <span class="problem-title">Gift Card Bundle Pair</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="ledger-cancellation-groups" data-difficulty="Medium" data-topics="Array|Two Pointers|Sorting">
+          <button class="problem-card" type="button" data-problem="ledger-cancellation-groups" data-difficulty="Medium">
             <span class="problem-title">Ledger Cancellation Groups</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="firmware-checksum-settling" data-difficulty="Easy" data-topics="Hash Table|Math|Two Pointers">
+          <button class="problem-card" type="button" data-problem="firmware-checksum-settling" data-difficulty="Easy">
             <span class="problem-title">Firmware Checksum Settling</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="distinct-keystroke-stretch" data-difficulty="Medium" data-topics="Hash Table|String|Sliding Window">
+          <button class="problem-card" type="button" data-problem="distinct-keystroke-stretch" data-difficulty="Medium">
             <span class="problem-title">Distinct Keystroke Stretch</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="required-marker-span" data-difficulty="Hard" data-topics="Hash Table|String|Sliding Window">
+          <button class="problem-card" type="button" data-problem="required-marker-span" data-difficulty="Hard">
             <span class="problem-title">Required Marker Span</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="packet-chunk-block-offsets" data-difficulty="Hard" data-topics="Hash Table|String|Sliding Window">
+          <button class="problem-card" type="button" data-problem="packet-chunk-block-offsets" data-difficulty="Hard">
             <span class="problem-title">Packet Chunk Block Offsets</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shortest-upload-batch" data-difficulty="Medium" data-topics="Array|Binary Search|Sliding Window|Prefix Sum">
+          <button class="problem-card" type="button" data-problem="shortest-upload-batch" data-difficulty="Medium">
             <span class="problem-title">Shortest Upload Batch</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="puzzle-grid-save-check" data-difficulty="Medium" data-topics="Array|Hash Table|Matrix">
+          <button class="problem-card" type="button" data-problem="puzzle-grid-save-check" data-difficulty="Medium">
             <span class="problem-title">Puzzle Grid Save Check</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="led-panel-ring-scan" data-difficulty="Medium" data-topics="Array|Matrix|Simulation">
+          <button class="problem-card" type="button" data-problem="led-panel-ring-scan" data-difficulty="Medium">
             <span class="problem-title">LED Panel Ring Scan</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sensor-frame-quarter-turn" data-difficulty="Medium" data-topics="Array|Math|Matrix">
+          <button class="problem-card" type="button" data-problem="sensor-frame-quarter-turn" data-difficulty="Medium">
             <span class="problem-title">Sensor Frame Quarter Turn</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="faulty-sensor-grid-blanking" data-difficulty="Medium" data-topics="Array|Hash Table|Matrix">
+          <button class="problem-card" type="button" data-problem="faulty-sensor-grid-blanking" data-difficulty="Medium">
             <span class="problem-title">Faulty Sensor Grid Blanking</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="microbe-culture-tick" data-difficulty="Medium" data-topics="Array|Matrix|Simulation">
+          <button class="problem-card" type="button" data-problem="microbe-culture-tick" data-difficulty="Medium">
             <span class="problem-title">Microbe Culture Tick</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="marquee-letter-tiles" data-difficulty="Easy" data-topics="Hash Table|String|Counting">
+          <button class="problem-card" type="button" data-problem="marquee-letter-tiles" data-difficulty="Easy">
             <span class="problem-title">Marquee Letter Tiles</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="anonymizer-substitution-audit" data-difficulty="Easy" data-topics="Hash Table|String">
+          <button class="problem-card" type="button" data-problem="anonymizer-substitution-audit" data-difficulty="Easy">
             <span class="problem-title">Anonymizer Substitution Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="log-line-shape-template" data-difficulty="Easy" data-topics="Hash Table|String">
+          <button class="problem-card" type="button" data-problem="log-line-shape-template" data-difficulty="Easy">
             <span class="problem-title">Log Line Shape Template</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="scrambled-label-match" data-difficulty="Easy" data-topics="Hash Table|String|Sorting">
+          <button class="problem-card" type="button" data-problem="scrambled-label-match" data-difficulty="Easy">
             <span class="problem-title">Scrambled Label Match</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="letter-rack-clusters" data-difficulty="Medium" data-topics="Array|Hash Table|String|Sorting">
+          <button class="problem-card" type="button" data-problem="letter-rack-clusters" data-difficulty="Medium">
             <span class="problem-title">Letter Rack Clusters</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="recent-card-repeat-alert" data-difficulty="Easy" data-topics="Array|Hash Table|Sliding Window">
+          <button class="problem-card" type="button" data-problem="recent-card-repeat-alert" data-difficulty="Easy">
             <span class="problem-title">Recent Card Repeat Alert</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="allocated-port-block" data-difficulty="Medium" data-topics="Array|Hash Table|Union Find">
+          <button class="problem-card" type="button" data-problem="allocated-port-block" data-difficulty="Medium">
             <span class="problem-title">Allocated Port Block</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="rack-slot-range-labels" data-difficulty="Easy" data-topics="Array">
+          <button class="problem-card" type="button" data-problem="rack-slot-range-labels" data-difficulty="Easy">
             <span class="problem-title">Rack Slot Range Labels</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="room-booking-busy-blocks" data-difficulty="Medium" data-topics="Array">
+          <button class="problem-card" type="button" data-problem="room-booking-busy-blocks" data-difficulty="Medium">
             <span class="problem-title">Room Booking Busy Blocks</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="batch-health-check-windows" data-difficulty="Medium" data-topics="Array|Greedy|Sorting">
+          <button class="problem-card" type="button" data-problem="batch-health-check-windows" data-difficulty="Medium">
             <span class="problem-title">Batch Health Check Windows</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="upload-location-normalizer" data-difficulty="Medium" data-topics="String|Stack">
+          <button class="problem-card" type="button" data-problem="upload-location-normalizer" data-difficulty="Medium">
             <span class="problem-title">Upload Location Normalizer</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="tentative-bid-ledger" data-difficulty="Medium" data-topics="Stack|Design">
+          <button class="problem-card" type="button" data-problem="tentative-bid-ledger" data-difficulty="Medium">
             <span class="problem-title">Tentative Bid Ledger</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="pricing-rule-bytecode" data-difficulty="Medium" data-topics="Array|Math|Stack">
+          <button class="problem-card" type="button" data-problem="pricing-rule-bytecode" data-difficulty="Medium">
             <span class="problem-title">Pricing Rule Bytecode</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="budget-sheet-formulas" data-difficulty="Hard" data-topics="Math|String|Stack|Recursion">
+          <button class="problem-card" type="button" data-problem="budget-sheet-formulas" data-difficulty="Hard">
             <span class="problem-title">Budget Sheet Formulas</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="workflow-handoff-loop" data-difficulty="Easy" data-topics="Hash Table|Linked List|Two Pointers">
+          <button class="problem-card" type="button" data-problem="workflow-handoff-loop" data-difficulty="Easy">
             <span class="problem-title">Workflow Handoff Loop</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="odometer-digit-chains" data-difficulty="Medium" data-topics="Linked List|Math|Recursion">
+          <button class="problem-card" type="button" data-problem="odometer-digit-chains" data-difficulty="Medium">
             <span class="problem-title">Odometer Digit Chains</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="replica-event-interleave" data-difficulty="Easy" data-topics="Linked List|Recursion">
+          <button class="problem-card" type="button" data-problem="replica-event-interleave" data-difficulty="Easy">
             <span class="problem-title">Replica Event Interleave</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="outline-snapshot-duplicator" data-difficulty="Medium" data-topics="Hash Table|Linked List">
+          <button class="problem-card" type="button" data-problem="outline-snapshot-duplicator" data-difficulty="Medium">
             <span class="problem-title">Outline Snapshot Duplicator</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="playlist-segment-flip" data-difficulty="Medium" data-topics="Linked List">
+          <button class="problem-card" type="button" data-problem="playlist-segment-flip" data-difficulty="Medium">
             <span class="problem-title">Playlist Segment Flip</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="radio-frame-batching" data-difficulty="Hard" data-topics="Linked List|Recursion">
+          <button class="problem-card" type="button" data-problem="radio-frame-batching" data-difficulty="Hard">
             <span class="problem-title">Radio Frame Batching</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="activity-feed-retraction" data-difficulty="Medium" data-topics="Linked List|Two Pointers">
+          <button class="problem-card" type="button" data-problem="activity-feed-retraction" data-difficulty="Medium">
             <span class="problem-title">Activity Feed Retraction</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="single-scan-badge-filter" data-difficulty="Medium" data-topics="Linked List|Two Pointers">
+          <button class="problem-card" type="button" data-problem="single-scan-badge-filter" data-difficulty="Medium">
             <span class="problem-title">Single Scan Badge Filter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="playlist-tail-wraparound" data-difficulty="Medium" data-topics="Linked List|Two Pointers">
+          <button class="problem-card" type="button" data-problem="playlist-tail-wraparound" data-difficulty="Medium">
             <span class="problem-title">Playlist Tail Wraparound</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="print-queue-triage" data-difficulty="Medium" data-topics="Linked List|Two Pointers">
+          <button class="problem-card" type="button" data-problem="print-queue-triage" data-difficulty="Medium">
             <span class="problem-title">Print Queue Triage</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="edge-thumbnail-store" data-difficulty="Medium" data-topics="Hash Table|Linked List|Design">
+          <button class="problem-card" type="button" data-problem="edge-thumbnail-store" data-difficulty="Medium">
             <span class="problem-title">Edge Thumbnail Store</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="fraud-rule-worst-case" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="fraud-rule-worst-case" data-difficulty="Easy">
             <span class="problem-title">Fraud Rule Worst Case</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="staging-drift-check" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="staging-drift-check" data-difficulty="Easy">
             <span class="problem-title">Staging Drift Check</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="right-to-left-layout" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="right-to-left-layout" data-difficulty="Easy">
             <span class="problem-title">Right To Left Layout</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="kiosk-panel-mirror-audit" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="kiosk-panel-mirror-audit" data-difficulty="Easy">
             <span class="problem-title">Kiosk Panel Mirror Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="crash-dump-index-rebuild" data-difficulty="Medium" data-topics="Array|Hash Table|Divide and Conquer|Tree|Binary Tree">
+          <button class="problem-card" type="button" data-problem="crash-dump-index-rebuild" data-difficulty="Medium">
             <span class="problem-title">Crash Dump Index Rebuild</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="query-parse-cache-restore" data-difficulty="Medium" data-topics="Array|Hash Table|Divide and Conquer|Tree|Binary Tree">
+          <button class="problem-card" type="button" data-problem="query-parse-cache-restore" data-difficulty="Medium">
             <span class="problem-title">Query Parse Cache Restore</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="org-chart-row-navigation" data-difficulty="Medium" data-topics="Linked List|Tree|DFS|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="org-chart-row-navigation" data-difficulty="Medium">
             <span class="problem-title">Org Chart Row Navigation</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="screen-reader-menu-chain" data-difficulty="Medium" data-topics="Linked List|Stack|Tree|DFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="screen-reader-menu-chain" data-difficulty="Medium">
             <span class="problem-title">Screen Reader Menu Chain</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="dungeon-route-budget" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="dungeon-route-budget" data-difficulty="Easy">
             <span class="problem-title">Dungeon Route Budget</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="menu-extension-checksum" data-difficulty="Medium" data-topics="Tree|DFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="menu-extension-checksum" data-difficulty="Medium">
             <span class="problem-title">Menu Extension Checksum</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="grid-segment-net-yield" data-difficulty="Hard" data-topics="Dynamic Programming|Tree|DFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="grid-segment-net-yield" data-difficulty="Hard">
             <span class="problem-title">Grid Segment Net Yield</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="ordered-index-cursor" data-difficulty="Medium" data-topics="Stack|Tree|Design|Binary Search Tree|Binary Tree|Iterator">
+          <button class="problem-card" type="button" data-problem="ordered-index-cursor" data-difficulty="Medium">
             <span class="problem-title">Ordered Index Cursor</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="heap-slot-census" data-difficulty="Medium" data-topics="Binary Search|Bit Manipulation|Tree|Binary Tree">
+          <button class="problem-card" type="button" data-problem="heap-slot-census" data-difficulty="Medium">
             <span class="problem-title">Heap Slot Census</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shared-approver-lookup" data-difficulty="Medium" data-topics="Tree|DFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="shared-approver-lookup" data-difficulty="Medium">
             <span class="problem-title">Shared Approver Lookup</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="collapsed-panel-labels" data-difficulty="Medium" data-topics="Tree|DFS|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="collapsed-panel-labels" data-difficulty="Medium">
             <span class="problem-title">Collapsed Panel Labels</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="hop-depth-signal-means" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="hop-depth-signal-means" data-difficulty="Easy">
             <span class="problem-title">Hop Depth Signal Means</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="rollout-wave-planner" data-difficulty="Medium" data-topics="Tree|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="rollout-wave-planner" data-difficulty="Medium">
             <span class="problem-title">Rollout Wave Planner</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="serpentine-tier-sweep" data-difficulty="Medium" data-topics="Tree|BFS|Binary Tree">
+          <button class="problem-card" type="button" data-problem="serpentine-tier-sweep" data-difficulty="Medium">
             <span class="problem-title">Serpentine Tier Sweep</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="tightest-channel-spacing" data-difficulty="Easy" data-topics="Tree|DFS|BFS|Binary Search Tree|Binary Tree">
+          <button class="problem-card" type="button" data-problem="tightest-channel-spacing" data-difficulty="Easy">
             <span class="problem-title">Tightest Channel Spacing</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="latency-rank-query" data-difficulty="Medium" data-topics="Tree|DFS|Binary Search Tree|Binary Tree">
+          <button class="problem-card" type="button" data-problem="latency-rank-query" data-difficulty="Medium">
             <span class="problem-title">Latency Rank Query</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="restored-index-integrity" data-difficulty="Medium" data-topics="Tree|DFS|BFS|Binary Search Tree|Binary Tree">
+          <button class="problem-card" type="button" data-problem="restored-index-integrity" data-difficulty="Medium">
             <span class="problem-title">Restored Index Integrity</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="copper-pad-continuity" data-difficulty="Medium" data-topics="Matrix|DFS|BFS|Union Find">
+          <button class="problem-card" type="button" data-problem="copper-pad-continuity" data-difficulty="Medium">
             <span class="problem-title">Copper Pad Continuity</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sealed-air-pocket-backfill" data-difficulty="Medium" data-topics="Matrix|DFS|BFS|Union Find">
+          <button class="problem-card" type="button" data-problem="sealed-air-pocket-backfill" data-difficulty="Medium">
             <span class="problem-title">Sealed Air Pocket Backfill</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sandbox-topology-replica" data-difficulty="Medium" data-topics="Hash Table|DFS|BFS|Graph">
+          <button class="problem-card" type="button" data-problem="sandbox-topology-replica" data-difficulty="Medium">
             <span class="problem-title">Sandbox Topology Replica</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="lab-unit-converter" data-difficulty="Medium" data-topics="Array|String|DFS|BFS|Union Find|Graph">
+          <button class="problem-card" type="button" data-problem="lab-unit-converter" data-difficulty="Medium">
             <span class="problem-title">Lab Unit Converter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="onboarding-track-feasibility" data-difficulty="Medium" data-topics="DFS|BFS|Graph|Topological Sort">
+          <button class="problem-card" type="button" data-problem="onboarding-track-feasibility" data-difficulty="Medium">
             <span class="problem-title">Onboarding Track Feasibility</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="migration-run-order" data-difficulty="Medium" data-topics="DFS|BFS|Graph|Topological Sort">
+          <button class="problem-card" type="button" data-problem="migration-run-order" data-difficulty="Medium">
             <span class="problem-title">Migration Run Order</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="portal-dice-race" data-difficulty="Medium" data-topics="Array|BFS|Matrix">
+          <button class="problem-card" type="button" data-problem="portal-dice-race" data-difficulty="Medium">
             <span class="problem-title">Portal Dice Race</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="approved-sequence-edits" data-difficulty="Medium" data-topics="Hash Table|String|BFS">
+          <button class="problem-card" type="button" data-problem="approved-sequence-edits" data-difficulty="Medium">
             <span class="problem-title">Approved Sequence Edits</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="hostname-rename-chain" data-difficulty="Hard" data-topics="Hash Table|String|BFS">
+          <button class="problem-card" type="button" data-problem="hostname-rename-chain" data-difficulty="Hard">
             <span class="problem-title">Hostname Rename Chain</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="command-palette-index" data-difficulty="Medium" data-topics="Hash Table|String|Design|Trie">
+          <button class="problem-card" type="button" data-problem="command-palette-index" data-difficulty="Medium">
             <span class="problem-title">Command Palette Index</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="crossword-pattern-matcher" data-difficulty="Medium" data-topics="String|DFS|Design|Trie">
+          <button class="problem-card" type="button" data-problem="crossword-pattern-matcher" data-difficulty="Medium">
             <span class="problem-title">Crossword Pattern Matcher</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="letter-grid-tracer" data-difficulty="Hard" data-topics="Array|String|Backtracking|Trie|Matrix">
+          <button class="problem-card" type="button" data-problem="letter-grid-tracer" data-difficulty="Hard">
             <span class="problem-title">Letter Grid Tracer</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="vanity-dial-expansion" data-difficulty="Medium" data-topics="Hash Table|String|Backtracking">
+          <button class="problem-card" type="button" data-problem="vanity-dial-expansion" data-difficulty="Medium">
             <span class="problem-title">Vanity Dial Expansion</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="canary-host-selection" data-difficulty="Medium" data-topics="Backtracking">
+          <button class="problem-card" type="button" data-problem="canary-host-selection" data-difficulty="Medium">
             <span class="problem-title">Canary Host Selection</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="startup-order-sweep" data-difficulty="Medium" data-topics="Array|Backtracking">
+          <button class="problem-card" type="button" data-problem="startup-order-sweep" data-difficulty="Medium">
             <span class="problem-title">Startup Order Sweep</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="freight-pallet-loadouts" data-difficulty="Medium" data-topics="Array|Backtracking">
+          <button class="problem-card" type="button" data-problem="freight-pallet-loadouts" data-difficulty="Medium">
             <span class="problem-title">Freight Pallet Loadouts</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="interference-free-towers" data-difficulty="Hard" data-topics="Backtracking">
+          <button class="problem-card" type="button" data-problem="interference-free-towers" data-difficulty="Hard">
             <span class="problem-title">Interference Free Towers</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="nesting-fuzzer-corpus" data-difficulty="Medium" data-topics="String|Dynamic Programming|Backtracking">
+          <button class="problem-card" type="button" data-problem="nesting-fuzzer-corpus" data-difficulty="Medium">
             <span class="problem-title">Nesting Fuzzer Corpus</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="letter-panel-tracing" data-difficulty="Medium" data-topics="Array|String|Backtracking|Matrix">
+          <button class="problem-card" type="button" data-problem="letter-panel-tracing" data-difficulty="Medium">
             <span class="problem-title">Letter Panel Tracing</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sensor-calibration-index" data-difficulty="Easy" data-topics="Array|Divide and Conquer|Tree|Binary Search Tree|Binary Tree">
+          <button class="problem-card" type="button" data-problem="sensor-calibration-index" data-difficulty="Easy">
             <span class="problem-title">Sensor Calibration Index</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="maintenance-window-consolidation" data-difficulty="Medium" data-topics="Array|Sorting">
+          <button class="problem-card" type="button" data-problem="maintenance-window-consolidation" data-difficulty="Medium">
             <span class="problem-title">Maintenance Window Consolidation</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="mirrored-tag-segment" data-difficulty="Medium" data-topics="String|Dynamic Programming|Two Pointers">
+          <button class="problem-card" type="button" data-problem="mirrored-tag-segment" data-difficulty="Medium">
             <span class="problem-title">Mirrored Tag Segment</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="sorted-schedule-slot" data-difficulty="Easy" data-topics="Array|Binary Search">
+          <button class="problem-card" type="button" data-problem="sorted-schedule-slot" data-difficulty="Easy">
             <span class="problem-title">Sorted Schedule Slot</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="serial-counter-advance" data-difficulty="Easy" data-topics="Array|Math">
+          <button class="problem-card" type="button" data-problem="serial-counter-advance" data-difficulty="Easy">
             <span class="problem-title">Serial Counter Advance</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="wide-register-arithmetic" data-difficulty="Easy" data-topics="Math|String|Bit Manipulation|Simulation">
+          <button class="problem-card" type="button" data-problem="wide-register-arithmetic" data-difficulty="Easy">
             <span class="problem-title">Wide Register Arithmetic</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="unmatched-badge-scan" data-difficulty="Easy" data-topics="Array|Bit Manipulation">
+          <button class="problem-card" type="button" data-problem="unmatched-badge-scan" data-difficulty="Easy">
             <span class="problem-title">Unmatched Badge Scan</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="symmetric-lottery-tickets" data-difficulty="Easy" data-topics="Math">
+          <button class="problem-card" type="button" data-problem="symmetric-lottery-tickets" data-difficulty="Easy">
             <span class="problem-title">Symmetric Lottery Tickets</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="robot-stride-plans" data-difficulty="Easy" data-topics="Math|Dynamic Programming|Memoization">
+          <button class="problem-card" type="button" data-problem="robot-stride-plans" data-difficulty="Easy">
             <span class="problem-title">Robot Stride Plans</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="integer-magnitude-estimator" data-difficulty="Easy" data-topics="Math|Binary Search">
+          <button class="problem-card" type="button" data-problem="integer-magnitude-estimator" data-difficulty="Easy">
             <span class="problem-title">Integer Magnitude Estimator</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="arrangement-count-suffix" data-difficulty="Medium" data-topics="Math">
+          <button class="problem-card" type="button" data-problem="arrangement-count-suffix" data-difficulty="Medium">
             <span class="problem-title">Arrangement Count Suffix</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="highway-billboard-leasing" data-difficulty="Medium" data-topics="Array|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="highway-billboard-leasing" data-difficulty="Medium">
             <span class="problem-title">Highway Billboard Leasing</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="trading-streak-report" data-difficulty="Medium" data-topics="Array|Divide and Conquer|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="trading-streak-report" data-difficulty="Medium">
             <span class="problem-title">Trading Streak Report</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="kiosk-token-payout" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Breadth-First Search">
+          <button class="problem-card" type="button" data-problem="kiosk-token-payout" data-difficulty="Medium">
             <span class="problem-title">Kiosk Token Payout</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="benchmark-progress-chain" data-difficulty="Medium" data-topics="Array|Binary Search|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="benchmark-progress-chain" data-difficulty="Medium">
             <span class="problem-title">Benchmark Progress Chain</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="paged-catalog-lookup" data-difficulty="Medium" data-topics="Array|Binary Search|Matrix">
+          <button class="problem-card" type="button" data-problem="paged-catalog-lookup" data-difficulty="Medium">
             <span class="problem-title">Paged Catalog Lookup</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="signal-crest-locator" data-difficulty="Medium" data-topics="Array|Binary Search">
+          <button class="problem-card" type="button" data-problem="signal-crest-locator" data-difficulty="Medium">
             <span class="problem-title">Signal Crest Locator</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shifted-price-snapshot" data-difficulty="Medium" data-topics="Array|Binary Search">
+          <button class="problem-card" type="button" data-problem="shifted-price-snapshot" data-difficulty="Medium">
             <span class="problem-title">Shifted Price Snapshot</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="conveyor-grid-routing" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Matrix">
+          <button class="problem-card" type="button" data-problem="conveyor-grid-routing" data-difficulty="Medium">
             <span class="problem-title">Conveyor Grid Routing</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="picking-robot-floor-plan" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Matrix">
+          <button class="problem-card" type="button" data-problem="picking-robot-floor-plan" data-difficulty="Medium">
             <span class="problem-title">Picking Robot Floor Plan</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="hashtag-vocabulary-splitter" data-difficulty="Medium" data-topics="Array|Hash Table|String|Dynamic Programming|Trie|Memoization">
+          <button class="problem-card" type="button" data-problem="hashtag-vocabulary-splitter" data-difficulty="Medium">
             <span class="problem-title">Hashtag Vocabulary Splitter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="permission-flag-counter" data-difficulty="Easy" data-topics="Divide and Conquer|Bit Manipulation">
+          <button class="problem-card" type="button" data-problem="permission-flag-counter" data-difficulty="Easy">
             <span class="problem-title">Permission Flag Counter</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="replica-write-audit" data-difficulty="Medium" data-topics="Array|Bit Manipulation">
+          <button class="problem-card" type="button" data-problem="replica-write-audit" data-difficulty="Medium">
             <span class="problem-title">Replica Write Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="address-block-shared-bits" data-difficulty="Medium" data-topics="Bit Manipulation">
+          <button class="problem-card" type="button" data-problem="address-block-shared-bits" data-difficulty="Medium">
             <span class="problem-title">Address Block Shared Bits</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="mine-level-descent" data-difficulty="Medium" data-topics="Array|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="mine-level-descent" data-difficulty="Medium">
             <span class="problem-title">Mine Level Descent</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="scanner-code-reconciliation" data-difficulty="Medium" data-topics="String|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="scanner-code-reconciliation" data-difficulty="Medium">
             <span class="problem-title">Scanner Code Reconciliation</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="rooftop-panel-footprint" data-difficulty="Medium" data-topics="Array|Dynamic Programming|Matrix">
+          <button class="problem-card" type="button" data-problem="rooftop-panel-footprint" data-difficulty="Medium">
             <span class="problem-title">Rooftop Panel Footprint</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="orbital-energy-window" data-difficulty="Medium" data-topics="Array|Divide and Conquer|Dynamic Programming|Queue|Monotonic Queue">
+          <button class="problem-card" type="button" data-problem="orbital-energy-window" data-difficulty="Medium">
             <span class="problem-title">Orbital Energy Window</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="ring-buffer-dump-lookup" data-difficulty="Medium" data-topics="Array|Binary Search">
+          <button class="problem-card" type="button" data-problem="ring-buffer-dump-lookup" data-difficulty="Medium">
             <span class="problem-title">Ring Buffer Dump Lookup</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="rating-leaderboard-cutoff" data-difficulty="Medium" data-topics="Array|Divide and Conquer|Sorting|Heap|Quickselect">
+          <button class="problem-card" type="button" data-problem="rating-leaderboard-cutoff" data-difficulty="Medium">
             <span class="problem-title">Rating Leaderboard Cutoff</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="log-timestamp-span" data-difficulty="Medium" data-topics="Array|Binary Search">
+          <button class="problem-card" type="button" data-problem="log-timestamp-span" data-difficulty="Medium">
             <span class="problem-title">Log Timestamp Span</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="compound-growth-factor" data-difficulty="Medium" data-topics="Math|Recursion">
+          <button class="problem-card" type="button" data-problem="compound-growth-factor" data-difficulty="Medium">
             <span class="problem-title">Compound Growth Factor</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shared-buffer-keystroke-audit" data-difficulty="Medium" data-topics="String|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="shared-buffer-keystroke-audit" data-difficulty="Medium">
             <span class="problem-title">Shared Buffer Keystroke Audit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="spot-capacity-round-trips" data-difficulty="Hard" data-topics="Array|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="spot-capacity-round-trips" data-difficulty="Hard">
             <span class="problem-title">Spot Capacity Round Trips</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="freight-slot-trading-limit" data-difficulty="Hard" data-topics="Array|Dynamic Programming">
+          <button class="problem-card" type="button" data-problem="freight-slot-trading-limit" data-difficulty="Hard">
             <span class="problem-title">Freight Slot Trading Limit</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="firmware-event-chain-ordering" data-difficulty="Medium" data-topics="Linked List|Two Pointers|Divide and Conquer|Sorting|Merge Sort">
+          <button class="problem-card" type="button" data-problem="firmware-event-chain-ordering" data-difficulty="Medium">
             <span class="problem-title">Firmware Event Chain Ordering</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="twin-sensor-midpoint-reading" data-difficulty="Hard" data-topics="Array|Binary Search|Divide and Conquer">
+          <button class="problem-card" type="button" data-problem="twin-sensor-midpoint-reading" data-difficulty="Hard">
             <span class="problem-title">Twin Sensor Midpoint Reading</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="survey-stake-alignment" data-difficulty="Hard" data-topics="Array|Hash Table|Math|Geometry">
+          <button class="problem-card" type="button" data-problem="survey-stake-alignment" data-difficulty="Hard">
             <span class="problem-title">Survey Stake Alignment</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="serial-link-word-mirror" data-difficulty="Easy" data-topics="Divide and Conquer|Bit Manipulation">
+          <button class="problem-card" type="button" data-problem="serial-link-word-mirror" data-difficulty="Easy">
             <span class="problem-title">Serial Link Word Mirror</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Easy</span>
           </button>
-          <button class="problem-card" type="button" data-problem="studio-contract-bankroll" data-difficulty="Hard" data-topics="Array|Greedy|Sorting|Heap">
+          <button class="problem-card" type="button" data-problem="studio-contract-bankroll" data-difficulty="Hard">
             <span class="problem-title">Studio Contract Bankroll</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="flight-combo-fare-shortlist" data-difficulty="Medium" data-topics="Array|Heap|Priority Queue">
+          <button class="problem-card" type="button" data-problem="flight-combo-fare-shortlist" data-difficulty="Medium">
             <span class="problem-title">Flight Combo Fare Shortlist</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="shard-result-consolidation" data-difficulty="Hard" data-topics="Linked List|Divide and Conquer|Heap|Merge Sort">
+          <button class="problem-card" type="button" data-problem="shard-result-consolidation" data-difficulty="Hard">
             <span class="problem-title">Shard Result Consolidation</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="live-clock-offset-monitor" data-difficulty="Hard" data-topics="Two Pointers|Design|Sorting|Heap|Data Stream">
+          <button class="problem-card" type="button" data-problem="live-clock-offset-monitor" data-difficulty="Hard">
             <span class="problem-title">Live Clock Offset Monitor</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Hard</span>
           </button>
-          <button class="problem-card" type="button" data-problem="terrain-mask-tiling" data-difficulty="Medium" data-topics="Array|Divide and Conquer|Matrix">
+          <button class="problem-card" type="button" data-problem="terrain-mask-tiling" data-difficulty="Medium">
             <span class="problem-title">Terrain Mask Tiling</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
           </button>
-          <button class="problem-card" type="button" data-problem="bounded-event-queue" data-difficulty="Medium" data-topics="Array|Design">
+          <button class="problem-card" type="button" data-problem="bounded-event-queue" data-difficulty="Medium">
             <span class="problem-title">Bounded Event Queue</span>
             <span class="problem-source" hidden></span>
             <span class="problem-meta">Medium</span>
diff --git a/web/practice-insights.js b/web/practice-insights.js
index 177a3c1f..f976c9b8 100644
--- a/web/practice-insights.js
+++ b/web/practice-insights.js
@@ -17,14 +17,13 @@ export function filterProblems(
 
 const ASSESSED = new Set(["HIRE", "NO_HIRE"]);
 
-export function recentPerformance(problems, reports, limit = 8) {
-  const topicsByProblem = new Map(
-    problems.map((problem) => [problem.id, problem.topics ?? []]),
-  );
+export function recentPerformance(reports, limit = 8) {
   const attempts = reports
     .filter(
       (entry) =>
-        Number.isFinite(entry.at) && ASSESSED.has(entry.report?.decision),
+        Number.isFinite(entry.at) &&
+        !entry.report?.incomplete &&
+        ASSESSED.has(entry.report?.decision),
     )
     .sort((left, right) => right.at - left.at)
     .slice(0, limit);
@@ -35,7 +34,7 @@ export function recentPerformance(problems, reports, limit = 8) {
   ).length;
   const topicResults = new Map();
   for (const entry of attempts) {
-    for (const topic of topicsByProblem.get(entry.problemId) ?? []) {
+    for (const topic of entry.report.topics ?? []) {
       const result = topicResults.get(topic) ?? { passes: 0, misses: 0 };
       result[entry.report.decision === "HIRE" ? "passes" : "misses"] += 1;
       topicResults.set(topic, result);
diff --git a/web/problem-data.js b/web/problem-data.js
index 8fd270b5..53b62085 100644
--- a/web/problem-data.js
+++ b/web/problem-data.js
@@ -17,6 +17,7 @@
 // those links without restoring duplicate problem files, and is fetched only
 // after the scenario-name lookup misses.
 let pageMap;
+let topicMap;
 
 const judges = new Map();
 
@@ -98,6 +99,17 @@ export function loadPageMap() {
   return pageMap;
 }
 
+/// The page-to-topic lookup is absent from the initial lobby HTML because it
+/// gives away the techniques behind every scenario. It arrives only after the
+/// candidate opens the problem picker to filter by topic.
+export function loadTopicMap() {
+  topicMap ??= fetchJson("/problem-topics.json").catch((error) => {
+    topicMap = undefined;
+    throw error;
+  });
+  return topicMap;
+}
+
 /// `page` is the problem's page name, the only name the browser uses for it.
 ///
 /// Null when the bank has no judge for this problem, which the runner reports
diff --git a/web/problem-picker.js b/web/problem-picker.js
index cf6414c4..7c658570 100644
--- a/web/problem-picker.js
+++ b/web/problem-picker.js
@@ -147,6 +147,8 @@ function step(level, by) {
 ///
 /// The optional clock keeps the scheduling rule deterministic in its tests.
 /// An explicit redraw avoids the current problem whenever another is available.
+/// `reviewProblems` stays broader than `problems` when an opt-in filter narrows
+/// new practice: a due review remains the first priority across those filters.
 export function pickProblem(
   problems,
   difficulties,
@@ -154,6 +156,7 @@ export function pickProblem(
   random = Math.random,
   now = Date.now(),
   avoid,
+  reviewProblems = problems,
 ) {
   const eligible = problems.filter((problem) =>
     difficulties.has(problem.difficulty),
@@ -165,7 +168,7 @@ export function pickProblem(
       .filter((entry) => entry?.report?.decision === "HIRE")
       .map((entry) => entry.problemId),
   );
-  const due = problems.filter((problem) => reviews.get(problem.id)?.due);
+  const due = reviewProblems.filter((problem) => reviews.get(problem.id)?.due);
   const fresh = eligible.filter((problem) => !passed.has(problem.id));
   const choices =
     [due, fresh, eligible]
diff --git a/web/problem-topics.json b/web/problem-topics.json
new file mode 100644
index 00000000..bfadcc0f
--- /dev/null
+++ b/web/problem-topics.json
@@ -0,0 +1,755 @@
+{
+  "template-delimiter-audit": [
+    "String",
+    "Stack"
+  ],
+  "chargeback-pair-match": [
+    "Array",
+    "Hash Table"
+  ],
+  "firmware-buffer-splice": [
+    "Array",
+    "Two Pointers",
+    "Sorting"
+  ],
+  "muted-alert-filter": [
+    "Array",
+    "Two Pointers"
+  ],
+  "telemetry-reading-dedupe": [
+    "Array",
+    "Two Pointers"
+  ],
+  "alert-digest-trimming": [
+    "Array",
+    "Two Pointers"
+  ],
+  "replica-quorum-version": [
+    "Array",
+    "Hash Table",
+    "Divide and Conquer",
+    "Counting"
+  ],
+  "carousel-slot-shift": [
+    "Array",
+    "Math",
+    "Two Pointers"
+  ],
+  "single-resale-window": [
+    "Array",
+    "Dynamic Programming"
+  ],
+  "single-slot-reseller": [
+    "Array",
+    "Dynamic Programming",
+    "Greedy"
+  ],
+  "relay-chain-reachability": [
+    "Array",
+    "Dynamic Programming",
+    "Greedy"
+  ],
+  "drone-pad-hopping": [
+    "Array",
+    "Dynamic Programming",
+    "Greedy"
+  ],
+  "package-impact-score": [
+    "Array",
+    "Sorting",
+    "Counting Sort"
+  ],
+  "backend-pool-sampler": [
+    "Array",
+    "Hash Table",
+    "Math",
+    "Design",
+    "Randomized"
+  ],
+  "pipeline-stage-gains": [
+    "Array",
+    "Prefix Sum"
+  ],
+  "circular-route-charging": [
+    "Array",
+    "Greedy"
+  ],
+  "shift-crew-bonus-points": [
+    "Array",
+    "Greedy"
+  ],
+  "terrain-runoff-pooling": [
+    "Array",
+    "Two Pointers",
+    "Dynamic Programming",
+    "Stack",
+    "Monotonic Stack"
+  ],
+  "archive-volume-numbers": [
+    "Hash Table",
+    "Math",
+    "String"
+  ],
+  "film-credits-year-stamp": [
+    "Hash Table",
+    "Math",
+    "String"
+  ],
+  "autocomplete-token-width": [
+    "String"
+  ],
+  "metric-namespace-root": [
+    "String",
+    "Trie"
+  ],
+  "backwards-caption-repair": [
+    "String",
+    "Two Pointers"
+  ],
+  "bouncing-print-head": [
+    "String"
+  ],
+  "firmware-signature-scan": [
+    "Two Pointers",
+    "String",
+    "String Matching"
+  ],
+  "thermal-receipt-layout": [
+    "Array",
+    "String",
+    "Simulation"
+  ],
+  "mirror-phrase-contest-filter": [
+    "Two Pointers",
+    "String"
+  ],
+  "ordered-event-trace-check": [
+    "Two Pointers",
+    "String",
+    "Dynamic Programming"
+  ],
+  "billboard-pole-banner": [
+    "Array",
+    "Two Pointers",
+    "Greedy"
+  ],
+  "gift-card-bundle-pair": [
+    "Array",
+    "Two Pointers",
+    "Binary Search"
+  ],
+  "ledger-cancellation-groups": [
+    "Array",
+    "Two Pointers",
+    "Sorting"
+  ],
+  "firmware-checksum-settling": [
+    "Hash Table",
+    "Math",
+    "Two Pointers"
+  ],
+  "distinct-keystroke-stretch": [
+    "Hash Table",
+    "String",
+    "Sliding Window"
+  ],
+  "required-marker-span": [
+    "Hash Table",
+    "String",
+    "Sliding Window"
+  ],
+  "packet-chunk-block-offsets": [
+    "Hash Table",
+    "String",
+    "Sliding Window"
+  ],
+  "shortest-upload-batch": [
+    "Array",
+    "Binary Search",
+    "Sliding Window",
+    "Prefix Sum"
+  ],
+  "puzzle-grid-save-check": [
+    "Array",
+    "Hash Table",
+    "Matrix"
+  ],
+  "led-panel-ring-scan": [
+    "Array",
+    "Matrix",
+    "Simulation"
+  ],
+  "sensor-frame-quarter-turn": [
+    "Array",
+    "Math",
+    "Matrix"
+  ],
+  "faulty-sensor-grid-blanking": [
+    "Array",
+    "Hash Table",
+    "Matrix"
+  ],
+  "microbe-culture-tick": [
+    "Array",
+    "Matrix",
+    "Simulation"
+  ],
+  "marquee-letter-tiles": [
+    "Hash Table",
+    "String",
+    "Counting"
+  ],
+  "anonymizer-substitution-audit": [
+    "Hash Table",
+    "String"
+  ],
+  "log-line-shape-template": [
+    "Hash Table",
+    "String"
+  ],
+  "scrambled-label-match": [
+    "Hash Table",
+    "String",
+    "Sorting"
+  ],
+  "letter-rack-clusters": [
+    "Array",
+    "Hash Table",
+    "String",
+    "Sorting"
+  ],
+  "recent-card-repeat-alert": [
+    "Array",
+    "Hash Table",
+    "Sliding Window"
+  ],
+  "allocated-port-block": [
+    "Array",
+    "Hash Table",
+    "Union Find"
+  ],
+  "rack-slot-range-labels": [
+    "Array"
+  ],
+  "room-booking-busy-blocks": [
+    "Array"
+  ],
+  "batch-health-check-windows": [
+    "Array",
+    "Greedy",
+    "Sorting"
+  ],
+  "upload-location-normalizer": [
+    "String",
+    "Stack"
+  ],
+  "tentative-bid-ledger": [
+    "Stack",
+    "Design"
+  ],
+  "pricing-rule-bytecode": [
+    "Array",
+    "Math",
+    "Stack"
+  ],
+  "budget-sheet-formulas": [
+    "Math",
+    "String",
+    "Stack",
+    "Recursion"
+  ],
+  "workflow-handoff-loop": [
+    "Hash Table",
+    "Linked List",
+    "Two Pointers"
+  ],
+  "odometer-digit-chains": [
+    "Linked List",
+    "Math",
+    "Recursion"
+  ],
+  "replica-event-interleave": [
+    "Linked List",
+    "Recursion"
+  ],
+  "outline-snapshot-duplicator": [
+    "Hash Table",
+    "Linked List"
+  ],
+  "playlist-segment-flip": [
+    "Linked List"
+  ],
+  "radio-frame-batching": [
+    "Linked List",
+    "Recursion"
+  ],
+  "activity-feed-retraction": [
+    "Linked List",
+    "Two Pointers"
+  ],
+  "single-scan-badge-filter": [
+    "Linked List",
+    "Two Pointers"
+  ],
+  "playlist-tail-wraparound": [
+    "Linked List",
+    "Two Pointers"
+  ],
+  "print-queue-triage": [
+    "Linked List",
+    "Two Pointers"
+  ],
+  "edge-thumbnail-store": [
+    "Hash Table",
+    "Linked List",
+    "Design"
+  ],
+  "fraud-rule-worst-case": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Tree"
+  ],
+  "staging-drift-check": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Tree"
+  ],
+  "right-to-left-layout": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Tree"
+  ],
+  "kiosk-panel-mirror-audit": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Tree"
+  ],
+  "crash-dump-index-rebuild": [
+    "Array",
+    "Hash Table",
+    "Divide and Conquer",
+    "Tree",
+    "Binary Tree"
+  ],
+  "query-parse-cache-restore": [
+    "Array",
+    "Hash Table",
+    "Divide and Conquer",
+    "Tree",
+    "Binary Tree"
+  ],
+  "org-chart-row-navigation": [
+    "Linked List",
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Tree"
+  ],
+  "screen-reader-menu-chain": [
+    "Linked List",
+    "Stack",
+    "Tree",
+    "DFS",
+    "Binary Tree"
+  ],
+  "dungeon-route-budget": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Tree"
+  ],
+  "menu-extension-checksum": [
+    "Tree",
+    "DFS",
+    "Binary Tree"
+  ],
+  "grid-segment-net-yield": [
+    "Dynamic Programming",
+    "Tree",
+    "DFS",
+    "Binary Tree"
+  ],
+  "ordered-index-cursor": [
+    "Stack",
+    "Tree",
+    "Design",
+    "Binary Search Tree",
+    "Binary Tree",
+    "Iterator"
+  ],
+  "heap-slot-census": [
+    "Binary Search",
+    "Bit Manipulation",
+    "Tree",
+    "Binary Tree"
+  ],
+  "shared-approver-lookup": [
+    "Tree",
+    "DFS",
+    "Binary Tree"
+  ],
+  "collapsed-panel-labels": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Tree"
+  ],
+  "hop-depth-signal-means": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Tree"
+  ],
+  "rollout-wave-planner": [
+    "Tree",
+    "BFS",
+    "Binary Tree"
+  ],
+  "serpentine-tier-sweep": [
+    "Tree",
+    "BFS",
+    "Binary Tree"
+  ],
+  "tightest-channel-spacing": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Search Tree",
+    "Binary Tree"
+  ],
+  "latency-rank-query": [
+    "Tree",
+    "DFS",
+    "Binary Search Tree",
+    "Binary Tree"
+  ],
+  "restored-index-integrity": [
+    "Tree",
+    "DFS",
+    "BFS",
+    "Binary Search Tree",
+    "Binary Tree"
+  ],
+  "copper-pad-continuity": [
+    "Matrix",
+    "DFS",
+    "BFS",
+    "Union Find"
+  ],
+  "sealed-air-pocket-backfill": [
+    "Matrix",
+    "DFS",
+    "BFS",
+    "Union Find"
+  ],
+  "sandbox-topology-replica": [
+    "Hash Table",
+    "DFS",
+    "BFS",
+    "Graph"
+  ],
+  "lab-unit-converter": [
+    "Array",
+    "String",
+    "DFS",
+    "BFS",
+    "Union Find",
+    "Graph"
+  ],
+  "onboarding-track-feasibility": [
+    "DFS",
+    "BFS",
+    "Graph",
+    "Topological Sort"
+  ],
+  "migration-run-order": [
+    "DFS",
+    "BFS",
+    "Graph",
+    "Topological Sort"
+  ],
+  "portal-dice-race": [
+    "Array",
+    "BFS",
+    "Matrix"
+  ],
+  "approved-sequence-edits": [
+    "Hash Table",
+    "String",
+    "BFS"
+  ],
+  "hostname-rename-chain": [
+    "Hash Table",
+    "String",
+    "BFS"
+  ],
+  "command-palette-index": [
+    "Hash Table",
+    "String",
+    "Design",
+    "Trie"
+  ],
+  "crossword-pattern-matcher": [
+    "String",
+    "DFS",
+    "Design",
+    "Trie"
+  ],
+  "letter-grid-tracer": [
+    "Array",
+    "String",
+    "Backtracking",
+    "Trie",
+    "Matrix"
+  ],
+  "vanity-dial-expansion": [
+    "Hash Table",
+    "String",
+    "Backtracking"
+  ],
+  "canary-host-selection": [
+    "Backtracking"
+  ],
+  "startup-order-sweep": [
+    "Array",
+    "Backtracking"
+  ],
+  "freight-pallet-loadouts": [
+    "Array",
+    "Backtracking"
+  ],
+  "interference-free-towers": [
+    "Backtracking"
+  ],
+  "nesting-fuzzer-corpus": [
+    "String",
+    "Dynamic Programming",
+    "Backtracking"
+  ],
+  "letter-panel-tracing": [
+    "Array",
+    "String",
+    "Backtracking",
+    "Matrix"
+  ],
+  "sensor-calibration-index": [
+    "Array",
+    "Divide and Conquer",
+    "Tree",
+    "Binary Search Tree",
+    "Binary Tree"
+  ],
+  "maintenance-window-consolidation": [
+    "Array",
+    "Sorting"
+  ],
+  "mirrored-tag-segment": [
+    "String",
+    "Dynamic Programming",
+    "Two Pointers"
+  ],
+  "sorted-schedule-slot": [
+    "Array",
+    "Binary Search"
+  ],
+  "serial-counter-advance": [
+    "Array",
+    "Math"
+  ],
+  "wide-register-arithmetic": [
+    "Math",
+    "String",
+    "Bit Manipulation",
+    "Simulation"
+  ],
+  "unmatched-badge-scan": [
+    "Array",
+    "Bit Manipulation"
+  ],
+  "symmetric-lottery-tickets": [
+    "Math"
+  ],
+  "robot-stride-plans": [
+    "Math",
+    "Dynamic Programming",
+    "Memoization"
+  ],
+  "integer-magnitude-estimator": [
+    "Math",
+    "Binary Search"
+  ],
+  "arrangement-count-suffix": [
+    "Math"
+  ],
+  "highway-billboard-leasing": [
+    "Array",
+    "Dynamic Programming"
+  ],
+  "trading-streak-report": [
+    "Array",
+    "Divide and Conquer",
+    "Dynamic Programming"
+  ],
+  "kiosk-token-payout": [
+    "Array",
+    "Dynamic Programming",
+    "Breadth-First Search"
+  ],
+  "benchmark-progress-chain": [
+    "Array",
+    "Binary Search",
+    "Dynamic Programming"
+  ],
+  "paged-catalog-lookup": [
+    "Array",
+    "Binary Search",
+    "Matrix"
+  ],
+  "signal-crest-locator": [
+    "Array",
+    "Binary Search"
+  ],
+  "shifted-price-snapshot": [
+    "Array",
+    "Binary Search"
+  ],
+  "conveyor-grid-routing": [
+    "Array",
+    "Dynamic Programming",
+    "Matrix"
+  ],
+  "picking-robot-floor-plan": [
+    "Array",
+    "Dynamic Programming",
+    "Matrix"
+  ],
+  "hashtag-vocabulary-splitter": [
+    "Array",
+    "Hash Table",
+    "String",
+    "Dynamic Programming",
+    "Trie",
+    "Memoization"
+  ],
+  "permission-flag-counter": [
+    "Divide and Conquer",
+    "Bit Manipulation"
+  ],
+  "replica-write-audit": [
+    "Array",
+    "Bit Manipulation"
+  ],
+  "address-block-shared-bits": [
+    "Bit Manipulation"
+  ],
+  "mine-level-descent": [
+    "Array",
+    "Dynamic Programming"
+  ],
+  "scanner-code-reconciliation": [
+    "String",
+    "Dynamic Programming"
+  ],
+  "rooftop-panel-footprint": [
+    "Array",
+    "Dynamic Programming",
+    "Matrix"
+  ],
+  "orbital-energy-window": [
+    "Array",
+    "Divide and Conquer",
+    "Dynamic Programming",
+    "Queue",
+    "Monotonic Queue"
+  ],
+  "ring-buffer-dump-lookup": [
+    "Array",
+    "Binary Search"
+  ],
+  "rating-leaderboard-cutoff": [
+    "Array",
+    "Divide and Conquer",
+    "Sorting",
+    "Heap",
+    "Quickselect"
+  ],
+  "log-timestamp-span": [
+    "Array",
+    "Binary Search"
+  ],
+  "compound-growth-factor": [
+    "Math",
+    "Recursion"
+  ],
+  "shared-buffer-keystroke-audit": [
+    "String",
+    "Dynamic Programming"
+  ],
+  "spot-capacity-round-trips": [
+    "Array",
+    "Dynamic Programming"
+  ],
+  "freight-slot-trading-limit": [
+    "Array",
+    "Dynamic Programming"
+  ],
+  "firmware-event-chain-ordering": [
+    "Linked List",
+    "Two Pointers",
+    "Divide and Conquer",
+    "Sorting",
+    "Merge Sort"
+  ],
+  "twin-sensor-midpoint-reading": [
+    "Array",
+    "Binary Search",
+    "Divide and Conquer"
+  ],
+  "survey-stake-alignment": [
+    "Array",
+    "Hash Table",
+    "Math",
+    "Geometry"
+  ],
+  "serial-link-word-mirror": [
+    "Divide and Conquer",
+    "Bit Manipulation"
+  ],
+  "studio-contract-bankroll": [
+    "Array",
+    "Greedy",
+    "Sorting",
+    "Heap"
+  ],
+  "flight-combo-fare-shortlist": [
+    "Array",
+    "Heap",
+    "Priority Queue"
+  ],
+  "shard-result-consolidation": [
+    "Linked List",
+    "Divide and Conquer",
+    "Heap",
+    "Merge Sort"
+  ],
+  "live-clock-offset-monitor": [
+    "Two Pointers",
+    "Design",
+    "Sorting",
+    "Heap",
+    "Data Stream"
+  ],
+  "terrain-mask-tiling": [
+    "Array",
+    "Divide and Conquer",
+    "Matrix"
+  ],
+  "bounded-event-queue": [
+    "Array",
+    "Design"
+  ]
+}