leetcode 28. Implement strStr() 实现strStr()

 1 class Solution {
 2 public:
 3     int strStr(string haystack, string needle) {
 4         if(needle.empty()) return 0;
 5         int m=haystack.size(),n=needle.size();
 6         int flag=-1;
 7         for(int i=0;i<=m-n;i++){
 8             if(haystack[i]==needle[0]){
 9                 flag=i;
10                 for(int j=1;j<n;j++){
11                     if(haystack[i+j]!=needle[j]){
12                         flag=-1;break;
13                     }
14                 }
15                 if(flag>-1) return flag;
16             }
17         }
18         return flag;
19     }
20 };