[LeetCode]Implement strStr()

 1 class Solution {
 2 public:
 3     int strStr(string haystack, string needle) {
 4         int sub_len = needle.size();
 5         int total_len = haystack.size();
 6         if (sub_len > total_len) {
 7             return -1;
 8         }
 9         
10         if (haystack == needle) {
11             return 0;
12         }
13         
14         int result = -1;
15         for (int i = 0; i <= total_len - sub_len; ++i) {
16             if (haystack.substr(i, sub_len) == needle) {
17                 result = i;
18                 break;
19             }
20         }
21         
22         return result;
23     }
24 };