leetcode: Implement strStr()

http://oj.leetcode.com/problems/implement-strstr/

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

思路：

太简单了，没什么好说的。

class Solution {
public:
    char *strStr(char *haystack, char *needle) {
        int len_haystack = strlen(haystack), len_needle = strlen(needle);
        
        if (0 == len_needle) {
            return haystack;
        }
        
        for (int i = 0; i <= (len_haystack - len_needle); ++i) {
            if (0 == strncmp(haystack + i, needle, len_needle)) {
                return haystack + i;
            }
        }
        
        return NULL;
    }
};