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()];
+ }
+}