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Question

I\'m trying to solve a question and my question here is why doesn\'t my solution work?. Here\'s the question and below\'s the answer.

Question taken fr

Answer 1

Here is my code to solve the problem. I use DP , I think it's clear to understand.

Written in Java

public class Solution {
        public int numDecodings(String s) {
            if(s == null || s.length() == 0){
                return 0;
            }
            int n = s.length();
            int[] dp = new int[n+1];
            dp[0] = 1;
            dp[1] = s.charAt(0) != '0' ? 1 : 0;

            for(int i = 2; i <= n; i++){
                int first = Integer.valueOf(s.substring(i-1,i));
                int second = Integer.valueOf(s.substring(i-2,i));
                if(first >= 1 && first <= 9){
                    dp[i] += dp[i-1];
                }
                if(second >= 10 && second <= 26){
                    dp[i] += dp[i-2];
                }

            }
            return dp[n];

        }

}