add: decodeWays solution

Author: Cyjin-jani

decode-ways/Cyjin-jani.js

@@ -0,0 +1,57 @@
+//! 다시 풀어야 하는 문제
+
+// Time limit 초과
+const numDecodings_timeLimit = function (s) {
+  let answer = 0;
+
+  function recursion(idx, remains) {
+    if (idx === remains.length) {
+      answer++;
+      return;
+    }
+
+    const one = remains.slice(idx, idx + 1);
+    if (+one >= 1 && +one <= 9) {
+      recursion(idx + 1, remains);
+    }
+
+    if (idx + 1 < remains.length) {
+      const two = remains.slice(idx, idx + 2);
+      if (+two >= 10 && +two <= 26) {
+        recursion(idx + 2, remains);
+      }
+    }
+  }
+
+  recursion(0, s);
+
+  return answer;
+};
+
+// 메모이제이션 적용
+const numDecodings = function (s) {
+  function recursion(idx, remains, memo = {}) {
+    if (idx === remains.length) return 1;
+
+    if (idx in memo) return memo[idx];
+
+    let answer = 0;
+
+    const one = remains.slice(idx, idx + 1);
+    if (+one >= 1 && +one <= 9) {
+      answer += recursion(idx + 1, remains, memo);
+    }
+
+    if (idx + 1 < remains.length) {
+      const two = remains.slice(idx, idx + 2);
+      if (+two >= 10 && +two <= 26) {
+        answer += recursion(idx + 2, remains, memo);
+      }
+    }
+
+    memo[idx] = answer;
+    return answer;
+  }
+
+  return recursion(0, s, {});
+};