C语言中带头双向循环链表基本操作的实现详解

目录

• 一、概念与结构
• 二、基本操作的实现
• 1.创建结点
• 2.初始化链表
• 3.打印链表
• 4.尾插
• 5.尾删
• 6.头插
• 7.头删
• 8.查找某个数并返回其指针
• 9.在某个位置之前插入
• 10.删除某个位置
• 11.判断链表是否为空
• 12.计算链表中有效值的个数
• 13.销毁链表
• 三、测试代码

一、概念与结构

无头单向非循环链表结构简单，一般不会单独用来存数据。实际中更多的是作为其他数据结构的子结构，如哈希桶、图的邻接表等等。而带头双向循环链表的结构较为复杂，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，虽然它的结构复杂但是因为结构优势用代码实现起来会变得简单。

二、基本操作的实现

1.创建结点

LTNode* BuyListNode(ListDataType x)
{
    LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));
    if (newnode == NULL)
    {
        perror("malloc");
        exit(-1);
    }
    newnode->val = x;
    newnode->prev = NULL;
    newnode->next = NULL;
    return newnode;
}

2.初始化链表

void ListInit(LTNode** pphead)//初始化
{
    *pphead = (LTNode*)malloc(sizeof(LTNode));
    *pphead = BuyListNode(-1);
    (*pphead)->next = *pphead;
    (*pphead)->prev = *pphead;
}
//LTNode* ListInit()//初始化
//{
//    LTNode* phead = BuyListNode(-1);//初始化时将头结点置为-1;
//    phead->next = phead;
//    phead->prev = phead;
//    return phead;
//}

初始化链表有两种方式，一种是有返回类型（注释部分），另一种是在初始化函数中给结构体开辟空间（不过注意参数要为二级指针）。因为是带头结点的循环链表，所以prev和next指针都指向自己。

3.打印链表

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

注意while循环的结束条件，保证能够打印链表中的所有有效值。要对头结点进行assert判断，不能为空。

4.尾插

void ListPushBack(LTNode* phead, ListDataType x)//尾插
{
    assert(phead);
    LTNode* newnode = BuyListNode(x);
    LTNode* tail = phead->prev;
    newnode->next = tail->next;
    phead->prev = newnode;
    newnode->prev = tail;
    tail->next = newnode;
    //ListInsert(phead, x);
}

5.尾删

void ListPopBack(LTNode* phead)//尾删
{
    assert(phead);
    assert(phead->next != phead);
    LTNode* prevnode = phead->prev;
    prevnode->prev->next = phead;
    phead->prev = prevnode->prev;
    free(prevnode);
    //ListErase(phead->prev);
}

尾删时要注意判断phead->next != phead，不能删除头结点，同时记得要free(prevnode)释放删除后的空间。

6.头插

void ListPushFront(LTNode* phead, ListDataType x)//头插
{
    assert(phead);
    LTNode* tail = phead->next;
    LTNode* newnode = BuyListNode(x);
    tail->prev = newnode;
    newnode->next = tail;
    newnode->prev = phead;
    phead->next = newnode;
    //ListInsert(phead->next,x);
}

7.头删

void ListPopFront(LTNode* phead)//头删
{
    assert(phead);
    assert(phead->next != phead);
    LTNode* tail = phead->next;
    phead->next = tail->next;
    tail->next->prev = phead;
    //ListErase(phead->next);
}

8.查找某个数并返回其指针

LTNode* ListFind(LTNode* phead, ListDataType x)//找某个数返回其指针
{
    assert(phead);
    LTNode* cur = phead->next;
    while (cur != phead)
    {
        if (cur->val == x)
        {
            return cur;
        }
        cur = cur->next;
    }
    return NULL;
}

9.在某个位置之前插入

void ListInsert(LTNode* pos, ListDataType x)//在pos之前插入
{
    assert(pos);
    LTNode* newnode = BuyListNode(x);
    LTNode* tail = pos->prev;
    tail->next = newnode;
    newnode->prev = tail;
    newnode->next = pos;
    pos->prev = newnode;
}

10.删除某个位置

void ListErase(LTNode* pos)//删除pos位置
{
    assert(pos);
    LTNode* prevnode = pos->prev;
    LTNode* nextnode = pos->next;
    free(pos);
    prevnode->next = nextnode;
    nextnode->prev = prevnode;
    /*pos->next->prev = pos->prev;
    pos->prev->next = pos->next;
    free(pos);*/
}

11.判断链表是否为空

bool ListEmpty(LTNode* phead)//判断是否为空,如果是空，返回true
{
    assert(phead);
    return phead->next == phead;
}

12.计算链表中有效值的个数

size_t ListSize(LTNode* phead)//计算链表中有效值的个数
{
    assert(phead);
    size_t size = 0;
    LTNode* tail = phead->next;
    while (tail != phead)
    {
        size++;
        tail = tail->next;
    }
    return size;
}

13.销毁链表

void ListDestroy(LTNode* phead)//销毁链表
{
    assert(phead);
    LTNode* tail = phead->next;
    while (tail != phead)
    {
        LTNode* nextnode = tail->next;
        free(tail);
        tail = nextnode;
    }
    free(phead);
}

销毁链表时要注意要保证每个结点都释放，同时最后也要将头结点释放free(phead)。

三、测试代码

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
typedef int ListDataType;
typedef struct ListNode {
	ListDataType val;
	struct ListNode* prev;
	struct ListNode* next;
}LTNode;
LTNode* BuyListNode(ListDataType x)
{
	LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));
	if (newnode == NULL)
	{
		perror("malloc");
		exit(-1);
	}
	newnode->val = x;
	newnode->prev = NULL;
	newnode->next = NULL;
	return newnode;
}
void ListInit(LTNode** pphead)//初始化
{
	*pphead = (LTNode*)malloc(sizeof(LTNode));
	*pphead = BuyListNode(-1);
	(*pphead)->next = *pphead;
	(*pphead)->prev = *pphead;
}
//LTNode* ListInit()//初始化
//{
//	LTNode* phead = BuyListNode(-1);//初始化时将头结点置为-1;
//	phead->next = phead;
//	phead->prev = phead;
//	return phead;
//}

void ListPrint(LTNode* phead)//打印
{
	assert(phead);
	LTNode* cur = phead->next;
	while (cur != phead)
	{
		printf("%d ", cur->val);
		cur = cur->next;
	}
	printf("\n");
}
void ListPushBack(LTNode* phead, ListDataType x)//尾插
{
	assert(phead);
	LTNode* newnode = BuyListNode(x);
	LTNode* tail = phead->prev;
	newnode->next = tail->next;
	phead->prev = newnode;
	newnode->prev = tail;
	tail->next = newnode;
	//ListInsert(phead, x);
}
void ListPopBack(LTNode* phead)//尾删
{
	assert(phead);
	assert(phead->next != phead);
	LTNode* prevnode = phead->prev;
	prevnode->prev->next = phead;
	phead->prev = prevnode->prev;
	free(prevnode);
	//ListErase(phead->prev);
}
void ListPushFront(LTNode* phead, ListDataType x)//头插
{
	assert(phead);
	LTNode* tail = phead->next;
	LTNode* newnode = BuyListNode(x);
	tail->prev = newnode;
	newnode->next = tail;
	newnode->prev = phead;
	phead->next = newnode;
	//ListInsert(phead->next,x);
}
void ListPopFront(LTNode* phead)//头删
{
	assert(phead);
	assert(phead->next != phead);
	LTNode* tail = phead->next;
	phead->next = tail->next;
	tail->next->prev = phead;
	//ListErase(phead->next);
}
LTNode* ListFind(LTNode* phead, ListDataType x)//找某个数返回其指针
{
	assert(phead);
	LTNode* cur = phead->next;
	while (cur != phead)
	{
		if (cur->val == x)
		{
			return cur;
		}
		cur = cur->next;
	}
	return NULL;
}
void ListInsert(LTNode* pos, ListDataType x)//在pos之前插入
{
	assert(pos);
	LTNode* newnode = BuyListNode(x);
	LTNode* tail = pos->prev;
	tail->next = newnode;
	newnode->prev = tail;
	newnode->next = pos;
	pos->prev = newnode;
}
void ListErase(LTNode* pos)//删除pos位置
{
	assert(pos);
	LTNode* prevnode = pos->prev;
	LTNode* nextnode = pos->next;
	free(pos);
	prevnode->next = nextnode;
	nextnode->prev = prevnode;
	/*pos->next->prev = pos->prev;
	pos->prev->next = pos->next;
	free(pos);*/
}
bool ListEmpty(LTNode* phead)//判断是否为空,如果是空，返回true
{
	assert(phead);
	return phead->next == phead;
}
size_t ListSize(LTNode* phead)//计算链表中有效值的个数
{
	assert(phead);
	size_t size = 0;
	LTNode* tail = phead->next;
	while (tail != phead)
	{
		size++;
		tail = tail->next;
	}
	return size;
}
void ListDestroy(LTNode* phead)//销毁链表
{
	assert(phead);
	LTNode* tail = phead->next;
	while (tail != phead)
	{
		LTNode* nextnode = tail->next;
		free(tail);
		tail = nextnode;
	}
	free(phead);
}
void TestList()
{
	//LTNode* plist = ListInit(&plist);
	LTNode* plist = NULL;
	ListInit(&plist);
	ListPushBack(plist, 100);
	ListPushBack(plist, 200);
	ListPushBack(plist, 300);
	ListPushBack(plist, 400);
	ListPushBack(plist, 500);
	ListPopBack(plist);
	ListPopBack(plist);
	ListPopBack(plist);
	ListPrint(plist);
	ListPushFront(plist, 1000);
	ListPushFront(plist, 2000);
	ListPushFront(plist, 3000);
	ListPopFront(plist);
	ListPopFront(plist);
	ListPrint(plist);
	LTNode* pos = ListFind(plist, 1000);
	if (pos != NULL)
	{
		ListInsert(pos, 500);
		ListErase(pos);
	}
	ListPrint(plist);
	if (!ListEmpty(plist))
		printf("%d\n", ListSize(plist));
}
int main()
{
	TestList();
	return 0;
}

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