Decode Ways

Decode Ways string

A message containing letters from A-Z is being encoded to numbers using the following mapping:

'A' -> 1
'B' -> 2
...
'Z' -> 26

Given an encoded message containing digits, determine the total number of ways to decode it.

For example, Given encoded message “12”, it could be decoded as “AB” (1 2) or “L” (12).

The number of ways decoding “12” is 2.

Decode Ways Solution

public class DecodeWays {
    public int numDecodings(String s) {
        int n = s.length();

        if(n == 0) {
            return 0;
        }

        int[] dp = new int[n + 1];
        dp[n] = 1;
        dp[n - 1] = s.charAt(n - 1) != '0' ? 1 : 0;

        for(int i = n - 2; i >= 0; i--) {
            if(s.charAt(i) == '0') {
                continue;
            } else {
                dp[i] = (Integer.parseInt(s.substring(i, i + 2)) <= 26) ? dp[i + 1] + dp[i + 2] : dp[i + 1];
            }
        }

        return dp[0];
    }
}

Last modified October 4, 2020