LeetCode 91. Decode Ways--动态规划DP的Python和Java解法

题目地址：

LeetCode 动态规划（Dynamic programming）系列题目:LeetCode 动态规划（Dynamic programming）系列题目

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).

python的动态规划解法：

class Solution:def numDecodings(self, s):dpi_1=0dp_i=int(s>'')before=''for d in s:dpi_1, dp_i, before = dp_i, (d>'0')*dp_i + (9<int(before+d)<27)*dpi_1, dreturn dp_i

java的解法：

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];}
}

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