利用c语言将两个循环单链表合并为一个循环单链表，且要求空间复杂度为O(1)，写出最简单的完整代码

#include <stdio.h>
#include <stdlib.h>

typedef struct Node {
    int data;
    struct Node *next;
} Node;

Node *merge(Node *head1, Node *head2) {
    if (head1 == NULL) return head2;
    if (head2 == NULL) return head1;

    Node *tail1 = head1->next;
    while (tail1->next != head1) tail1 = tail1->next;
    tail1->next = head2->next;
    free(head2);
    return head1;
}

int main() {
    Node *head1 = (Node*)malloc(sizeof(Node));
    head1->data = 1;
    head1->next = (Node*)malloc(sizeof(Node));
    head1->next->data = 3;
    head1->next->next = (Node*)malloc(sizeof(Node));
    head1->next->next->data = 5;
    head1->next->next->next = head1;

    Node *head2 = (Node*)malloc(sizeof(Node));
    head2->data = 2;
    head2->next = (Node*)malloc(sizeof(Node));
    head2->next->data = 4;
    head2->next->next = (Node*)malloc(sizeof(Node));
    head2->next->next->data = 6;
    head2->next->next->next = head2;

    Node *head = merge(head1, head2);
    Node *p = head;
    do {
        printf("%d ", p->data);
        p = p->next;
    } while (p != head);
    printf("\n");

    return 0;
}