前言

各位小伙伴大家好，即上回的单向链表之后，双向链表来了，他和单向链表的主要区别就是，他有两个指针，同时指向前面一个节点，和后面一个节点，简直是完美，几乎解决的单向链表的大多数难题

1、初步认识双向链表

1.1 定义：

双向链表也叫双链表，是链表的一种，它的每个数据结点中都有两个指针，分别指向前面一个节点和后面一个节点。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。

1.2 结构

这是带头的双向循环链表。

1.3 节点的存储

typedef int DLDataType;typedef struct LinkNode
{DLDataType data;struct LinkNode* next;struct LinkNode* prv;
}LNode;

2、双向链表的接口函数

2.1 链表的节点的动态申请

LTNode* LTFound(DLDataType x)
{LTNode* newNode = (LTNode*)malloc(sizeof(LTNode));if (newNode == NULL){perror("LTInit()::malloc()");return;}newNode->next = newNode->prv = newNode;newNode->data = x;return newNode;
}

2.2 链表的初始化

// 法一：
LTNode* LTInit()
{LTNode* newhead = LTFound(-1);return newhead;
}
法二：
void LTInit(LTNode** pphead)
{LTNode* newhead = LTFound(-1);*phead = newhead;
}

2.3 尾插

void LTPushBack(LTNode* phead, DLDataType x)
{assert(phead);LTNode* cmp = LTFound(x);// phead phead->prv cmpcmp->next = phead;cmp->prv = phead->prv;phead->prv->next = cmp;phead->prv = cmp;
}

尾插这个节点不管是插入在头节点的前面还是尾节点后面都是一样的

2.4 头插

//头插
void LTPushFront(LTNode* phead, DLDataType x)
{assert(phead);LTNode* tmp = LTFound(x);// phead tmp phead->nexttmp->next = phead->next;tmp->prv = phead;phead->next = tmp;phead->next->prv = tmp;
}

头插必须插入在头节点的后面才是头插，头节点就是哨兵卫，链表进行操作的时候不能操作哨兵卫，否则就不带头了。

2.5 头删

//头删
void LTPopFront(LTNode* phead)
{assert(phead && phead->next != phead);LTNode* cur = phead->next;// phead  cur cur->nextphead->next = cur->next;cur->next = phead;free(cur);cur = NULL;
}

2.5 尾删

//尾删
void LTPopBack(LTNode* phead)
{assert(phead && phead->next != phead);LTNode* cur = phead->prv;// phead cur->prv curphead->prv = cur->prv;cur->prv->next = phead;free(cur);cur = NULL;
}

2.6 在pos节点后面添加数据

//在pos位置之后插入数据
void LTInsert(LTNode* pos, DLDataType x)
{assert(pos);LTNode* cur = LTCreate(x);// pos cur pos->nextcur->next = pos->next;cur->prv = pos;pos->next = cur;pos->next->prv = cur;}

2.6 删除pos节点

//删除pos节点
void LTErase(LTNode* pos)
{assert(pos);// pos->prv pos pos->nextpos->prv->next = pos->next;pos->next->prv = pos->prv;free(pos);pos = NULL;
}

3、双向链表的实现：

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <stdbool.h>
#include <string.h>typedef int DLDataType;typedef struct LinkNode
{DLDataType data;struct LinkNode* next;struct LinkNode* prv;
}LTNode;//双链表的节点创建
LTNode* LTCreate(DLDataType x)
{LTNode* newNode = (LTNode*)malloc(sizeof(LTNode));if (newNode == NULL){perror("LTInit()::malloc()");exit(-1);}newNode->next = newNode;newNode->prv = newNode;newNode->data = x;return newNode;
}//初始化
//void LTInit(LTNode** pphead)
//{
//	LTNode* newhead = LTFound(-1);
//}LTNode* LTInit()
{LTNode* newhead = LTCreate(-1);return newhead;
}//销毁链表
void LTDesTroy(LTNode* phead)
{assert(phead);LTNode* cur = phead->next;while (cur != phead){LTNode* next = cur->next;free(cur);cur = next;}free(phead);phead = NULL;
}//链表的打印
void LTPrint(LTNode* phead)
{LTNode* cur = phead->next;while (cur != phead){printf("%d->", cur->data);cur = cur->next;}printf("NULL\n");
}//查找pos节点
LTNode* LTFind(LTNode* phead, DLDataType x)
{assert(phead);LTNode* cur = phead->next;while (cur != phead){if (cur->data == x){return cur;}cur = cur->next;}return NULL;
}//插入数据之前，链表必须初始化到只有一个头结点的情况
//不改变哨兵位的地址，因此传一级即可
//尾插
void LTPushBack(LTNode* phead, DLDataType x)
{assert(phead);LTNode* cmp = LTCreate(x);// phead phead->prv cmpcmp->next = phead;cmp->prv = phead->prv;phead->prv->next = cmp;phead->prv = cmp;
}//头插
void LTPushFront(LTNode* phead, DLDataType x)
{assert(phead);LTNode* tmp = LTCreate(x);// phead tmp phead->nexttmp->next = phead->next;tmp->prv = phead;phead->next = tmp;phead->next->prv = tmp;
}//尾删
void LTPopBack(LTNode* phead)
{assert(phead && phead->next != phead);LTNode* cur = phead->prv;// phead cur->prv curphead->prv = cur->prv;cur->prv->next = phead;free(cur);cur = NULL;
}//头删
void LTPopFront(LTNode* phead)
{assert(phead && phead->next != phead);LTNode* cur = phead->next;// phead  cur cur->nextphead->next = cur->next;cur->next = phead;free(cur);cur = NULL;
}//在pos位置之后插入数据
void LTInsert(LTNode* pos, DLDataType x)
{assert(pos);LTNode* cur = LTCreate(x);// pos cur pos->nextcur->next = pos->next;cur->prv = pos;pos->next = cur;pos->next->prv = cur;}//删除pos节点
void LTErase(LTNode* pos)
{assert(pos);// pos->prv pos pos->nextpos->prv->next = pos->next;pos->next->prv = pos->prv;free(pos);pos = NULL;
}void DLinkListText()
{LTNode* phead = LTInit();LTPushBack(phead, 1);LTPushBack(phead, 2);LTPushBack(phead, 3);LTPrint(phead);LTPushFront(phead, 0);LTPushFront(phead, 999);LTPrint(phead);// LTPopFront(phead);// LTPrint(phead);LTPopBack(phead);LTPrint(phead);LTDesTroy(phead);
}int main()
{DLinkListText();return 0;
}