#include <bits/stdc++.h>
using namespace std;
typedef struct DNode{
    int data;
    DNode *prior,*next; 
}DNode,*DLinkList;
//初始化双链表 
bool InitDLinkList(DLinkList &L)
{
    L = (DNode*)malloc(sizeof(DNode));
    if(L == NULL) return false;
    L -> prior = NULL;
    L -> next = NULL;
    return true;
}
//判空 
bool Empty(DLinkList L)
{
    if(L -> next == NULL)
        return true;
    return false;
}
//后插 在指定结点p后插入结点s
bool InsertNextDNode(DLinkList &L,DNode *p,DNode *s)
{
    if(p == NULL || s == NULL)
        return false;
    s -> next = p -> next;
    if(p -> next != NULL)
        p -> next -> prior = s;
    s -> prior = p;
    p -> next = s;
    return true;
}
//前插 (找到p的前驱结点进行后插即可)
bool InsertPriorDNode(DLinkList &L,DNode *p,DNode *s)
{
    return InsertNextDNode(L,p->prior,s);
} 
//删除p结点的后继 不需要传入链表 只要有p结点的指针就能找到其后继 
bool DeleteNextNode(DNode *p)
{
    if(p == NULL) return false;
    DNode *q = p -> next;
    if(q == NULL) return false;
    p -> next = q -> next;
    if(q -> next != NULL) //别忘记特判 
        q -> next -> prior = p;
    free(q);
    return true;
} 
//销毁双链表
void DestoryList(DLinkList &L)
{
    while(L -> next != NULL)
        DeleteNextNode(L);
    free(L);
    L = NULL; 
}
void print(DLinkList &L)
{
    DNode *p = L;
    while(p -> next != NULL)
    {
        p = p -> next;
        cout << p -> data << ' ';
    }
    cout << endl;
    return;
}
int main()
{
    DLinkList L;
    InitDLinkList(L);
    cout << Empty(L) << endl;
    DNode *s = (DNode*)malloc(sizeof(DNode));
    s -> data = 6;
    s -> next = NULL;
    s -> prior = NULL;
    InsertNextDNode(L,L,s);
    print(L);
    DNode *p = (DNode*)malloc(sizeof(DNode));
    p -> data = 3;
    InsertPriorDNode(L,s,p);
    print(L);
    DeleteNextNode(L);
    print(L);
    DestoryList(L);
    return 0;
}