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

typedef struct Node {
    int data;
    struct Node *prior, *next;
} DNode, *DLinkList;

int InitList() {
    DNode *l = (DNode *)malloc(sizeof(DNode));
    if (l == NULL) return -1;
    l->prior = l;
    l->next = l;
    return 1;
}

int InsertNextNode(DNode *p, DNode *s) {
    if (p == NULL || s == NULL) return -1;
    s->next = p->next;
    p->next->prior = s;
    s->prior = p;
    p->next = s;
    return 1;
}

int DeleteNextNode(DNode *p) {
    if (p == NULL) return -1;
    DNode *q = p->next;
    p->next = q->next;
    q->next->prior = p;
    free(q);
    return 1;
}

int Empty(DLinkList l) {
    if (l->next == l) return 1;
    else return -1;
}

int isTail(DLinkList l, DNode *p) {
    if (p->next == l) return 1;
    else return -1;
}