Update 91-decode-ways.js

Author: everthis

91-decode-ways.js

@@ -1,3 +1,27 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+const numDecodings = function(s) {
+  if(s == null || s.length === 0) return 1
+  if(s[0] === '0') return 0
+  const set = new Set()
+  const n = s.length
+  for(let i = 1; i <= 26; i++) {
+    set.add(`${i}`)
+  }
+  const dp = Array(n + 1).fill(0)
+  dp[0] = dp[1] = 1
+  for(let i = 2; i <= n; i++) {
+    if(set.has(s[i - 2] + s[i - 1])) dp[i] += dp[i - 2]
+    if(set.has(s[i - 1])) dp[i] += dp[i - 1]
+  }
+  return dp[n]
+};
+
+
+// another
+
 /**
  * @param {string} s
  * @return {number}