feat: 91. Decode Ways

Author: gwbaik9717

decode-ways/gwbaik9717.js

@@ -0,0 +1,38 @@
+// Time complexity: O(n)
+// Space complexity: O(n)
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var numDecodings = function (s) {
+  const n = s.length;
+  const dp = Array.from({ length: n + 2 }, () => 0);
+  dp[1] = 1;
+
+  for (let i = 2; i < n + 2; i++) {
+    // 한자리
+    const charCode = Number(s[i - 2]);
+
+    if (charCode > 0) {
+      dp[i] += dp[i - 1];
+    }
+
+    // 두자리
+    if (i <= 2) {
+      continue;
+    }
+
+    if (Number(s[i - 3]) == 0) {
+      continue;
+    }
+
+    const strCode = Number(s.slice(i - 3, i - 1));
+
+    if (strCode > 0 && strCode <= 26) {
+      dp[i] += dp[i - 2];
+    }
+  }
+
+  return dp.at(-1);
+};