decode-ways

Author: jun0811

decode-ways/jun0811.js

@@ -0,0 +1,32 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+
+function check(str) {
+  if (str.length == 2) {
+    if (str[0] == '0') return false;
+  }
+  if (str >= 1 && str <= 26) return true;
+  return false;
+}
+
+var numDecodings = function (s) {
+  if (s[0] == '0') return 0;
+  const dp = [1, 1];
+
+  for (let i = 2; i <= s.length; i++) {
+    let tmp = dp[i - 1] + dp[i - 2];
+
+    // 2글자 체크 -> dp[i-2]을 뺴줌
+    const two_c = String(s[i - 2]) + String(s[i - 1]);
+    if (!check(two_c)) tmp -= dp[i - 2];
+
+    // 1글자 체크 -> dp[i-1]을 빼줌
+    if (!check(s[i - 1])) tmp -= dp[i - 1];
+
+    if (tmp == 0) return 0;
+    dp[i] = tmp;
+  }
+  return dp[s.length];
+};