Create 91-decode-ways.js

Author: everthis

91-decode-ways.js

@@ -0,0 +1,20 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+const numDecodings = function(s) {
+  if (s.length === 0) return 0
+  const N = s.length
+  const dp = Array(N + 1).fill(0)
+  dp[0] = 1
+  dp[1] = s[0] === "0" ? 0 : 1
+  for (let i = 2; i <= N; i++) {
+    if (s[i - 1] !== "0") {
+      dp[i] += dp[i - 1]
+    }
+    if (s[i - 2] === "1" || (s[i - 2] === "2" && s[i - 1] <= "6")) {
+      dp[i] += dp[i - 2]
+    }
+  }
+  return dp[N]
+}