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.

Update (2014-11-02):
The signature of the function had been updated to return the index instead of the pointer. If you still see your function signature returns a char * or String, please click the reload button  to reset your code definition.

class Solution {
public:
    int strStr(char *haystack, char *needle) {
    if(haystack==NULL||needle==NULL)return -1;
    int len1=strlen(haystack);
    int len2=strlen(needle);
    if(len1<len2)return -1;
    int i=0;
    for(;i<(len1-len2+1);i++)
    {
        int j=0;
        for(;j<len2;j++)
        {
            if(haystack[i+j]!=needle[j])
                break;
        }
        if(j==len2)return i;
    } 
    return -1;
    }
};