Merge pull request #2454 from grapefruit13/main

Author: grapefruit13

combination-sum/grapefruit13.ts

@@ -0,0 +1,20 @@
+function combinationSum(candidates: number[], target: number): number[][] {
+  const answer: number[][] = [];
+
+  function dfs(index: number, path: number[], sum: number) {
+    if (sum === target) {
+      answer.push([...path]);
+      return;
+    }
+    if (sum > target) return;
+
+    for (let i = index; i < candidates.length; i++) {
+      path.push(candidates[i]);            
+      dfs(i, path, sum + candidates[i]);   
+      path.pop();                          
+    }
+  }
+
+  dfs(0, [], 0);
+  return answer;
+}

decode-ways/grapefruit13.ts

@@ -0,0 +1,23 @@
+function numDecodings(s: string): number {
+    if (s[0]==="0") return 0;
+
+    const dp = new Array(s.length).fill(0);
+    dp[0] = 1;
+
+    for (let i=1; i<s.length; i++) {
+        if (s[i] !== "0") {
+            dp[i] += dp[i-1];
+        }
+
+        const two = Number(s[i-1] + s[i]);
+
+        if (10 <= two && two <= 26) {
+            if (i === 1) {
+                dp[i] += 1;
+            } else {
+                dp[i] += dp[i-2];
+            }
+        }
+    }
+    return dp[s.length - 1];
+};

valid-palindrome/grapefruit13.ts

@@ -0,0 +1,13 @@
+function isPalindrome(s: string): boolean {
+    const cleaned = s.toLowerCase().replace(/[^a-z0-9]/g, '');
+
+    let left = 0;
+    let right = cleaned.length - 1;
+
+    while (left < right) {
+        if (cleaned[left] !== cleaned[right]) return false;
+        left++;
+        right--;
+    }
+    return true;
+}