題目：https://leetcode.com/problems/decode-ways/description/
題意：讓你判斷字串可能有多少解碼方式
思路：
當前字元為’0’，則dp[i] = dp[i-2]
當前字元不為’0’，小於等於26，dp[i] = dp[i-1] + dp[2]; 大於26，dp[i] = dp[i-1]
程式碼：

class Solution {
public:
    int numDecodings(string s) {
        if(s == "")
            return 0;
        int dp[s.size()+1] = {1};
        for(int i = 1;i <= s.size();i++){
            if(s[i-1] != '0')
                dp[i] += dp[i-1];
            if(i >= 2){
                if(s[i-2] == '1' || (s[i-2] == '2' && s[i-1] <= '6'))
                    dp[i] += dp[i-2];
            }
        }
        return dp[s.size()];
    }
};