解码方法

public class Solution {
/*
* @param s: a string, encoded message
* @return: an integer, the number of ways decoding
*/
public int numDecodings(String s) {
// write your code here
int size = s.size();
if(size == 0)
return 0;

    int *dp = new int[size];
    dp[0] = 1*(s[0]!='0');
    if(size >= 2)
    {
        string t = s.substr(0,2);
        int n = atoi(t.c_str());
        dp[1] = dp[0]*(s[1]!='0') +  (n>0 && n<=26);

        for(int i=2; i<size; i++)
       {
           string t = s.substr(i-1,2);
           int n = atoi(t.c_str());
           dp[i] = dp[i-1]*(s[i]!='0') + (n>=10 && n<=26)*dp[i-2];
       }
    }
    return dp[size-1];
}

};