Leetcode---Implement strStr()

Implement strStr().

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

我试着用了最简单的匹配，居然过了，以后再用KMP之类的好好研究一下。

char *strStr(char *haystack, char *needle) {
        if(haystack==NULL || needle==NULL)
            return NULL;
        char * head=haystack;

        while(head!='\0'){
            char *p0=head;
            char * p=needle;
            while(*p!='\0' && *p0!='\0'){
                if(*p!=*p0){
                    break;
                }
                p++;
                p0++;
            }
            if(*p=='\0'){
                return head;
            }
            if(*p0=='\0'){
                return NULL;
            }
            head++;
        }
        return NULL;
    }