Leetcode: Decode Ways

 is being encoded to numbers using the following mapping:

, it could be decoded as  (1 2) or  (12).
 is 2.
dp:
int numDecodings(string s) { // Start typing your C/C++ solution below // DO NOT write int main() function int length = s.size(); if(length<1)return 0;int* dp = new int[length+1];memset(dp, 0, sizeof(int)*(length+1));dp[0] = 1;if(s[0] == '0')dp[1] = 0;else dp[1] = 1;for(int i = 2; i <= length; ++i){ int num = stoi(s.substr(i-1,1)); if(num > 0)dp[i] = dp[i-1];num = stoi(s.substr(i-2,2));if(num > 9 && num < 27)dp[i] += dp[i-2];}int res = dp[length];delete[] dp;return res; }