Day 106

Ways to Decode.java

@@ -0,0 +1,24 @@
+public class Solution {
+    public int numDecodings(String A) {
+        int n = A.length();
+        long[] dp = new long[n + 1];
+        dp[0] = 1;
+        if (A.charAt(0) != '0')
+            dp[1] = 1;
+        else
+            return 0;
+        for (int i = 1; i < n; i++) {
+            if (A.charAt(i) != '0')
+                dp[i + 1] = dp[i];
+            int num = Integer.parseInt(A.substring(i - 1, i + 1));
+            if (num >= 10 && num <= 26)
+                dp[i + 1] += dp[i - 1];
+
+            dp[i + 1] %= 1000000007;
+            if (A.charAt(i) == '0' && (num > 26 || num < 10)) 
+                return 0;
+        }
+        return (int) dp[n];
+    }
+}
+