Add 91_Decode_Ways.java

Author: Sean Prashad

Dynamic Programming/91_Decode_Ways.java

@@ -0,0 +1,22 @@
+class Solution {
+    public int numDecodings(String s) {
+        int[] dp = new int[s.length() + 1];
+        dp[0] = 1;
+        dp[1] = s.charAt(0) != '0' ? 1 : 0;
+
+        for (int i = 2; i <= s.length(); i++) {
+            int oneDigit = Integer.valueOf(s.substring(i - 1, i));
+            int twoDigits = Integer.valueOf(s.substring(i - 2, i));
+
+            if (1 <= oneDigit && oneDigit <= 9) {
+                dp[i] += dp[i - 1];
+            }
+
+            if (10 <= twoDigits && twoDigits <= 26) {
+                dp[i] += dp[i - 2];
+            }
+        }
+
+        return dp[s.length()];
+    }
+}