decode ways solution

Author: jinvicky

decode-ways/jinvicky.java

@@ -0,0 +1,23 @@
+class Solution {
+    public int numDecodings(String s) {
+        if (s.charAt(0) == '0') return 0;
+
+        int n = s.length();
+        int[] dp = new int[n+1];
+        dp[0] = dp[1] = 1;
+
+        for(int i = 2; i <= n; i++) {
+            int one = Character.getNumericValue(s.charAt(i-1));
+            int two = Integer.parseInt(s.substring(i-2, i));
+
+            if(1 <= one && one <= 9) {
+                dp[i] += dp[i-1];
+            }
+            if(10 <= two && two <= 26) {
+                dp[i] += dp[i-2];
+            }
+        }
+
+        return dp[n];
+    }
+}