decode ways solution

Author: krokerdile

decode-ways/krokerdile.js

@@ -0,0 +1,27 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var numDecodings = function(s) {
+    const n = s.length;
+    const memo = {};
+
+    function dfs(index) {
+        if (index === n) return 1;
+        if (s[index] === '0') return 0;
+        if (memo.hasOwnProperty(index)) return memo[index];
+
+        let count = dfs(index + 1);
+        if (index + 1 < n) {
+            const twoDigit = parseInt(s.slice(index, index + 2));
+            if (twoDigit >= 10 && twoDigit <= 26) {
+                count += dfs(index + 2);
+            }
+        }
+
+        memo[index] = count;
+        return count;
+    }
+
+    return dfs(0);
+};