1 class Solution { 2 public: 3     int numDecodings(string s) { 4         if(s == "") 5             return 0; 6         vector<int> count; 7         int i; 8         for(i = 0 ; i < s.length() ; ++i) 9         {10             count.push_back(0);11             if(s[i] < ‘0‘ || s[i] > ‘9‘)12                 return 0;13             if(s[i] == ‘0‘)14             {15                 if (i == 0 || s[i - 1] == ‘0‘ || s[i - 1] > ‘2‘) {  16                     return 0;  17                 }  18                 else {  19                     count[i] = i > 1 ? count[i - 2] : 1;  20                 }  21             }22             else23             {24                 if(i == 0)25                     count[i] = 1;26                 else27                 {28                     if(s[i] > ‘0‘)29                         count[i] = count[i-1];30                     if(i >= 1 &&(s[i-1] == ‘1‘ || (s[i-1] == ‘2‘ && s[i] < ‘7‘)))31                         count[i] += i>1 ? count[i-2]:1;    32                 }33             }34         }35         return count[s.length()-1];36     }37 };