Add decode ways solution - s0ooo0k

Author: s0ooo0k

decode-ways/s0ooo0k.java

@@ -0,0 +1,22 @@
+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]=1;
+        dp[1]=1;
+
+        for(int i=2; i<=n; i++) {
+            if(s.charAt(i-1)!='0') dp[i]+=dp[i-1];
+
+            int group = Integer.parseInt(s.substring(i-2, i));
+            if(group>=10 && group<=26) {
+                dp[i]+=dp[i-2];
+            }
+        }
+        return dp[n];
+    }
+}
+