带头双向循环链表（C语言实现）

带头双向循环链表概念及结构

概念：带头双向循环链表结构最复杂，一般用在单独存储数据。实际中使用的链表数据结构，都是带头双向循环链表。另外这个结构虽然结构复杂，但是使用代码实现以后会发现结构会带来很多优势，实现反而简单了。

带头双向循环链表的实现

List.h代码实现

#pragma once

#include 
#include 
#include 

typedef int LTDataType;
typedef struct ListNode
{
	LTDataType val;
	struct ListNode* next;
	struct ListNode* prev;
}LTNode;
LTNode* BuyLTNode(LTDataType x);//创建一个新的节点
void ListPrint(LTNode* plist);//打印
LTNode* ListInit();//初始化
void ListPushBack(LTNode* plist, LTDataType x); //尾插
void ListPopBack(LTNode* plist);//尾删
void ListPushFront(LTNode* plist, LTDataType x);//头插
void ListPopFront(LTNode* plist);//头删
LTNode* ListFind(LTNode* plist, LTDataType x);//查找
void ListInsert(LTNode* pos, LTDataType x);//在pos的前面进行插入
void ListErese(LTNode* pos);//删除pos位置的节点
void ListDestory(LTNode* plist);//销毁

List.c代码实现

#include "List.h"
LTNode* BuyLTNode(LTDataType x)
{
	LTNode* newnode = (LTNode*) malloc(sizeof(LTNode));
	if (newnode == NULL)
	{
		printf("malloc fail\n");
		exit(-1);
	}
	newnode->val = x;
	newnode->next = NULL;
	newnode->prev = NULL;
	return newnode;
}

void ListPrint(LTNode* plist)
{
	assert(plist);
	LTNode* cur = plist->next;
	while (cur != plist)
	{
		printf("%d ", cur->val);
		cur = cur->next;
	}
	printf("\n");
}

LTNode* ListInit()
{
	LTNode* plist = BuyLTNode(0);
	plist->next = plist;
	plist->prev = plist;
	return plist;
}
void ListDestory(LTNode* plist)
{
	assert(plist);
	LTNode* cur = plist->next;
	while (cur != plist)
	{
		LTNode* next = cur->next;
		free(cur);
		cur = next;
	}
	free(plist);
}

尾插：将尾节点的next连接到新的节点，将新节点的前驱连接到尾节点，然后将新节点的next连接到head，将head的前驱连接到新节点即可完成。

 代码实现：

void ListPushBack(LTNode* plist, LTDataType x)
{
	assert(plist);
	LTNode* newnode = BuyLTNode(x);
	LTNode* Tail = plist->prev;
	Tail->next = newnode;
	newnode->prev = Tail;
	plist->prev = newnode;
	newnode->next = plist;
}

尾删：将尾节点的前驱当做新的尾，与head建立连接，将旧尾free掉。

 代码实现：

void ListPopBack(LTNode* plist)
{
	assert(plist);
	assert(plist->next != plist);
	LTNode* Tail = plist->prev;
	LTNode* TailPrev = Tail->prev;
	free(Tail);
	Tail = NULL;
	TailPrev->next = plist;
	plist->prev = TailPrev;
}

头插：

 代码实现：

void ListPushFront(LTNode* plist, LTDataType x)
{
	assert(plist);
	LTNode* newnode = BuyLTNode(x);
	plist->next->prev = newnode;
	newnode->next = plist->next;
	plist->next = newnode;
	newnode->prev = plist;
}

头删：

代码实现： 

void ListPopFront(LTNode* plist)
{
	assert(plist);
	assert(plist->next != plist);
	LTNode* HeadNext = plist->next;
	HeadNext->next->prev = plist;
	plist->next = HeadNext->next;
	free(HeadNext);
	HeadNext = NULL;
}

查找代码实现：

LTNode* ListFind(LTNode* plist, LTDataType x)
{
	assert(plist);
	LTNode* cur = plist->next;
	while (cur != plist)
	{
		if (cur->val == x)
		{
			return cur;
		}
		cur = cur->next;
	}
	return NULL;
}

pos位置插入代码实现：

void ListInsert(LTNode* pos, LTDataType x)
{
	assert(pos);
	LTNode* newnode = BuyLTNode(x);
	LTNode* posPrev = pos->prev;

	newnode->next = pos;
	pos->prev = newnode;
	posPrev->next = newnode;
	newnode->prev = posPrev;
}

pos位置删除代码实现：

void ListErese(LTNode* pos)
{
	assert(pos);

	LTNode* posPrev = pos->prev;
	LTNode* posNext = pos->next;
	posPrev->next = posNext;
	posNext->prev = posPrev;
	free(pos);
	pos = NULL;
}

销毁代码实现：

void ListDestory(LTNode* plist)
{
	assert(plist);
	LTNode* cur = plist->next;
	while (cur != plist)
	{
		LTNode* next = cur->next;
		free(cur);
		cur = next;
	}
	free(plist);
}