91. Decode Ways

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.

• 这道题目比较怪异并不是特别需要技巧的题目。

class Solution {public:    int numDecodings(string s) {        int n = s.size();        vector<int> dp(n+1,0);        if(n <= 0){            return 0;        }        dp[n] = 1;        dp[n-1] = (s[n-1] == '0')?0:1;        for(int i = n-2;i >= 0;i--){            if(s[i] == '0'){                continue;                //dp[i] = dp[i+11];            }else{                int number = (s[i] - '0')*10 + s[i+1] - '0';                dp[i] = (number <= 26) ? (dp[i+1] + dp[i+2]):dp[i+1];            }            //cout<<"dp["<<i<<"] = "<<dp[i]<<endl;        }        return dp[0];    }};