Decode Ways

class Solution {public:    int numDecodings(string s) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if (s.size()==0) {            return 0;        }        vector<int> way(s.size()+1, 1);        for (int i=s.size()-1; i>=0; i--) {            if (s[i]!='0') {                way[i]=way[i+1];            }else {                way[i]=0;            }            if (s.size()-i>1 && (s[i]=='1' || (s[i]=='2' && s[i+1]>='0' && s[i+1]<='6'))) {                way[i]+=way[i+2];            }        }        return way[0];    }};

DP  Iteration