Decode Ways

Author: casentino

decode-ways/casentino.ts

@@ -0,0 +1,21 @@
+function numDecodings(s: string): number {
+  if (s.length === 1 && s[0] !== "0") {
+    return 1;
+  }
+  if (s[0] === "0") {
+    return 0;
+  }
+  const dp = new Array(s.length + 1).fill(0);
+  dp[0] = 1;
+  dp[1] = 1;
+  for (let i = 2; i <= s.length; i++) {
+    if (s[i - 1] !== "0") {
+      dp[i] += dp[i - 1];
+    }
+    const doubleNum = parseInt(s[i - 2] + s[i - 1]);
+    if (doubleNum >= 10 && doubleNum <= 26) {
+      dp[i] += dp[i - 2];
+    }
+  }
+  return dp[s.length];
+}