请用C语言实现strstr函数，至少使用两种方法

方法1：暴力匹配

char* my_strstr(char* haystack, char* needle) {
    if (!*needle) return haystack;
    char* p1 = haystack;
    while (*p1) {
        char* p1_begin = p1, *p2 = needle;
        while (*p1 && *p2 && *p1 == *p2) {
            p1++;
            p2++;
        }
        if (!*p2) return p1_begin;
        p1 = p1_begin + 1;
    }
    return NULL;
}

方法2：KMP算法

void compute_prefix(char* pattern, int* prefix) {
    int i = 1, j = 0;
    prefix[0] = 0;
    while (pattern[i]) {
        if (pattern[i] == pattern[j]) {
            j++;
            prefix[i] = j;
            i++;
        } else if (j > 0) {
            j = prefix[j - 1];
        } else {
            prefix[i] = 0;
            i++;
        }
    }
}

char* my_strstr(char* haystack, char* needle) {
    if (!*needle) return haystack;
    int n = strlen(haystack), m = strlen(needle);
    int prefix[m];
    compute_prefix(needle, prefix);
    int i = 0, j = 0;
    while (i < n) {
        if (haystack[i] == needle[j]) {
            i++;
            j++;
        } else if (j > 0) {
            j = prefix[j - 1];
        } else {
            i++;
        }
        if (j == m) return haystack + i - m;
    }
    return NULL;
}