Easy 9 Implement strStr()（28）

Description
Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Solution
暴力法。

class Solution {
public:
    int strStr(string haystack, string needle) {
     if(haystack.empty()&&needle.empty()) return  0; 
     int m=haystack.size(),n=needle.size();

     for(int i=0;i<=m-n;i++){
         int j=0;
         for(;j<n;j++){
             if(needle[j]!=haystack[i+j]) break;
         }
         if(j==n) return i;
     }
     return -1;
    }
};