Leetcode: Implement strStr()

class Solution
{
public:
    int strStr(char *haystack, char *needle)
    {

        int i,j;  
        for (i = j = 0; haystack[i] && needle[j];) {  
            if (haystack[i] == needle[j]) {  
                ++i;  
                ++j;  
            } else {  
                i = i - j + 1;  
                j = 0;  
            }  
        }  
        return needle[j] ? -1 : i - j;
    }
};