数据结构-单链表回环函数判断

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define size 4
int swap(int source[], int a, int b) {
    int temp;
    temp = source[a];
    source[a] = source[b];
    source[b] = temp;
    return 0;
}
typedef struct node {
    int data;
    struct node *next;
}linklist;

linklist *creatlist(int n) {
    linklist *p, *head, *q;
    int i;
    head = (linklist *)malloc(sizeof(linklist));
    head->data = 1;
    q = head;
    for (i = 2; i <= n; i++) {
        p = (linklist *)malloc(sizeof(linklist));
        p->data = i;
        q->next = p;
        q = p;
    }
    q->next = NULL;

    return head;

}
linklist *judge(linklist *head)
{
    if (head == NULL | head->next == NULL) {
        return 0;
    }
    linklist *p, *q;
    p = head->next;
    q = head->next->next;
    while (q  && q->next && p != q) {
        p = p->next;
        q = q->next->next;

    }
    if (p == q) {
        printf("this is a 回环链表 \n");
    }
    else printf("this is not 回环链表 \n");
    return 0;
}

int main()
{
    linklist *head, *now;
    head = creatlist(8);
    now = head;
    int i;
    for (i = 0; i < 8; i++) {
        printf("%d ", now->data);
        now = now->next;
    }
    printf("\n");
    now = head;
    judge(now);
}