Create 0091_Decode_Ways.java

Author: mkhuzaima

Diff for: 0091_Decode_Ways.java

@@ -0,0 +1,25 @@
+// id: 91
+// Name: Decode Ways
+// link: https://leetcode.com/problems/decode-ways
+// Difficulty: Medium
+
+class Solution {
+    public int numDecodings(String s) {
+        int dp1 = s.charAt(s.length()-1) == '0' ? 0: 1;
+        int dp2 = 1; // empty string
+
+        for (int i = s.length()-2; i >= 0; i--) {
+            int current = 0;
+            if (s.charAt(i) != '0') {
+                current += dp1;
+
+                if (Integer.parseInt(s.substring(i, i+2)) <= 26) {
+                    current += dp2;
+                }
+            }
+            dp2 = dp1;
+            dp1 = current;
+        }
+        return dp1;
+    }
+}