LeetCode刷题Medium篇Decode Ways(没有明白)

题目

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

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

Given a non-empty string containing only digits, determine the total number of ways to decode it.

Example 1:

Input: "12"
Output: 2
Explanation: It could be decoded as "AB" (1 2) or "L" (12).

Example 2:

Input: "226"
Output: 3
Explanation: It could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).

解法

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

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转载自blog.csdn.net/hanruikai/article/details/86505369