LeetCode ImplementStrstr

class Solution {
public:
    char *strStr(char *haystack, char *needle) {
        if (haystack == NULL || needle == NULL) return NULL;
        int wpos[256];
        char cur = 0;
        int len = 0;
        for (int i=0; i < 256; i++) wpos[i] = -1;

        for (int i=0; (cur =  needle[i]) != ‘\0‘; i++, len++) wpos[cur] = i;
        int p = 0, q = 0;
        while (true) {
            while (haystack[p] != ‘\0‘
                    && needle[q] != ‘\0‘
                    && haystack[p] == needle[q]) p++, q++;

            if ( needle[q] == ‘\0‘) {
                return haystack + p - q;
            }

            if (haystack[p] == ‘\0‘) {
                return NULL;
            }

            int npos = p - q + len;
            int move = wpos[haystack[npos]];
            q = 0;
            if (move < 0) {
                p++;
            } else {
                p = npos - move;
            }
        }
        return NULL;
    }
};