Leetcode91. Decode Ways

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.

代码（c++）：

class Solution {public:int numDecodings(string s) {if(s[0] == '0') return 0;if(s.length() == 1) return 1;int decode1, decode2;decode1 = 1;if((s[0] == '1') || (s[0] == '2' && s[1]-'0' <= 6)){if(s[1] == '0') decode2 = 1;else decode2 = 2;}else if(s[1] == '0') return 0;else decode2 = 1;for(int i = 2; i < s.length(); i++){int temp = decode2;if((s[i-1] == '1') || (s[i-1] == '2' && s[i]-'0' <= 6)) {if(s[i] != '0') decode2 = decode1 * 2 + (decode2 - decode1);else decode2 = decode1;}else if(s[i] == '0') return 0;decode1 = temp;}return decode2;}
};

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Leetcode91. Decode Ways

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