数据结构-双向循环链表的增删改查

List.h

#pragma once
#include 
#include 
#include 
#include 

typedef int LDataType;
typedef struct ListNode
{
	LDataType data;
	struct ListNode* pre;
	struct ListNode* next;
}LNode;

LNode* LInit();//链表的初始化
void LPushBack(LNode* phead, LDataType x);//双向链表的尾插
void LPushFront(LNode* phead, LDataType x);//双向链表的头插
LNode* LPopBack(LNode* phead);//双向链表的尾删
LNode* LPopFront(LNode* phead);//双向链表的头删
LNode* LFind(LNode* phead, LDataType x);//双向链表的查找
void LInsert(LNode* pos, LDataType x);//在pos之前插入
void LErase(LNode* pos);//删除pos位置的结点
void LDestroy(LNode* phead);//销毁链表

List.c

#define _CRT_SECURE_NO_WARNINGS 1
#include "List.h"
void Print(LNode* phead)
{
	LNode* p = phead->next;
	while (p != phead)
	{
		printf("%d<=>", p->data);
		p = p->next;
	}
	printf("NULL\n");
}
LNode* ByNode(LDataType x)
{
	LNode* ptr = (LNode*)malloc(sizeof(LNode));
	if (ptr == NULL)
	{
		perror("ByNode Fail::");
		return;
	}
	ptr->pre = NULL;
	ptr->next = NULL;
	ptr->data = x;
	return ptr;
}
LNode* LInit()
{
	LNode* phead = ByNode(-1);
	phead->next = phead;
	phead->pre = phead;
	return phead;
}

void LPushBack(LNode* phead, LDataType x)
{
	assert(phead);
	LNode* newnode = ByNode(x);
	LNode* tail = phead->pre;
	tail->next = newnode;
	newnode->pre = tail;
	newnode->next = phead;
	phead->pre = newnode;
	tail = newnode;
}

void LPushFront(LNode* phead, LDataType x)
{
	assert(phead);
	LNode* newnode = ByNode(x);
	newnode->next = phead->next;
	phead->next->pre = newnode;
	newnode->pre = phead;
	phead->next = newnode;
}
void LErase(LNode* pos)
{
	assert(pos);
	pos->pre->next = pos->next;
	pos->next->pre = pos->pre;
	free(pos);
}
LNode* LPopBack(LNode* phead)
{
	assert(phead);
	/*
	LNode* tail = phead->pre;
	phead->pre = tail->pre;
	tail->next = NULL;
	tail->pre->next = phead;
	tail->pre = NULL;
	free(tail);
	tail = phead->pre;
	*/
	LErase(phead->pre);
}
LNode* LPopFront(LNode* phead) 
{
	  assert(phead);
	//LNode* next = phead->next;
	//phead->next = next->next;
	//phead->next->pre = phead;
	只需要修改两个指针即可，剩下的两个next的指针会直接随着next的free消失。
	//free(next);
	LErase(phead -> next);
}
LNode* LFind(LNode* phead, LDataType x)
{
	assert(phead);
	LNode* cur = phead->next;
	while (cur!=phead)
	{
		if (cur->data == x)
			return cur;
		cur = cur->next;
	}
	return NULL;
}
void LInsert(LNode* pos, LDataType x)
{
	assert(pos);
	LNode* pre = pos->pre;
	LNode* newnode = ByNode(x);
	newnode->next = pos;
	pos->pre = newnode;
	pre->next = newnode;
	newnode->pre = pre; 
}
void LDestroy(LNode* phead)
{
	LNode* cur = phead->next;
	while (phead->next!=phead)
	{
		LErase(phead->next);
	}
}

test.c

#define _CRT_SECURE_NO_WARNINGS 1
#include "List.h"

void test1()
{
	LNode* plist = LInit();
	LPushBack(plist, 0);
	LPushBack(plist, 7);
	LPushBack(plist, 2);
	LPushBack(plist, 0);
	LPopBack(plist);
	LPopFront(plist);
	Print(plist);
	LDestroy(plist);
	Print(plist);
}
int main()
{
	test1();
	return 0;
}