【LeetCode】28 - Implement strStr()

Implement strStr().

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

Solution: 

 class Solution {
 public:
     int strStr(string haystack, string needle) {    //runtime:4ms
         int len1=haystack.size(), len2=needle.size();
         for(int i=;i<=len1-len2;i++)
         {
             int j=;
             for(;j<len2;j++){
                 if(haystack[i+j]!=needle[j])break;
             }
             if(j==len2)return i;
         }
         return -;
     }
 };