LeetCode--Decode Ways

 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             else
23             {
24                 if(i == 0)
25                     count[i] = 1;
26                 else
27                 {
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 };