双链表增删查改

链表是物理储存上非连续、非顺序的储存结构，逻辑上是连续的，通过指针链接次序实现的

链表又分为单向和双向，带头和不带头，循环和不循环，那下面我们要着重带头双向循环链表

那就让我们先看一下带头双向循环链表的基本示意图

 我们再看一下单向链表  

两个一比较，就很容易发现双向结构更复杂，在实际当中往往双向运用的更多，所以不要看它复杂，用起来反而更轻松，不说多话，咱们接着往下看

这是声明部分，方便我们了解各个部分的作用

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include<stdbool.h>

typedef int variety;
typedef struct ListNode
{
	struct ListNode* next;
	struct ListNode* prev;
	variety data;
}LTNode;

LTNode* Inital();//初始化
bool LTEmpty(LTNode* phead);//判空
void FrontInsert(LTNode* phead, variety x);//头插
void Print(LTNode* phead);//打印
void BackInsert(LTNode* phead, variety x);//尾插
void FrontDelete(LTNode* phead);//头删
void BackDelete(LTNode* phead);//尾删
LTNode* Find(LTNode* phead, variety x);//查找
void LTInsert(LTNode* pos, variety x);//在pos之前插入
void LTDelete(LTNode* pos);//pos位置删除
void Destroy(LTNode* phead);//销毁

初始化之前先看一下 ，先开辟一下节点，因为在插入方面用的到

LTNode* BuyTNode(variety x)
{
	LTNode* newnode = (LTNode*)malloc(sizeof(LTNode));
	if (newnode == NULL)
	{
		printf("malloc fail");
		return NULL;
	}
	newnode->data = x;
	newnode->next = NULL;
	newnode->prev = NULL;
	return newnode;
}

 声明之后我们还要具体运用，也就是定义，咱们要一步一步走，不然吃成大胖子，还怎么往后走，先看初始化部分

LTNode* Inital()
{
	LTNode* phead = BuyTNode(-1);
	phead->next = phead;
	phead->prev = phead;
	return phead;
}

 判空

bool LTEmpty(LTNode* phead)
{
	assert(phead);

	return phead->next == phead;
}

头插

void FrontInsert(LTNode* phead, variety x)
{
	assert(phead);
	LTNode* newnode = BuyTNode(x);
	LTNode* first = phead->next;

	phead->next = newnode;
	newnode->prev = phead;

	newnode->next = first;
	first->prev = newnode;

	/*LTInsert(phead->next, x);*/
}

 那这个是怎么实现的，想肯定是想不出来的，那咱们就用图来表示，这里phead表示哨兵位，看作没有，看成进行中转的作用

 

尾插 

void BackInsert(LTNode* phead, variety x)
{
	assert(phead);
	/*LTInsert(phead, x);*/
	LTNode* tail = phead->prev;
	LTNode* newnode = BuyTNode(x);
	tail->next = newnode;
	newnode->prev = tail;
	newnode->next = phead;
	phead->prev = newnode;
}

下图就能很明确表示

 头删

void FrontDelete(LTNode* phead)
{
	assert(phead);
	assert(!LTEmpty(phead));
	/*LTDelete(phead->next);*/
	LTNode* first = phead->next;
	LTNode* second = first->next;
	phead->next = second;
	second->prev = phead;
	free(first);
}

尾删 

void BackDelete(LTNode* phead)
{
	assert(phead);
	assert(!LTEmpty(phead));
	/*LTDelete(phead->prev);*/
	LTNode* tail = phead->prev;
	LTNode* tailPrev = tail->prev;
	free(tail);
	tailPrev->next = phead;
	phead->prev = tailPrev;
}

 

打印

void Print(LTNode* phead)
{
	assert(phead);
	printf("guard<==>");
	LTNode* cur = phead->next;
	while (cur != phead)
	{
		printf("%d<==>", cur->data);
		cur = cur->next;
	}
	printf("\n");
}

查找 

LTNode* Find(LTNode* phead, variety x)
{
	assert(phead);

	LTNode* cur = phead->next;
	while (cur != phead)
	{
		if (cur->data == x)
		{
			return cur;
		}

		cur = cur->next;
	}

	return NULL;
}

 在pos前插入

void LTInsert(LTNode* pos, variety x)
{
	assert(pos);
	LTNode* prev = pos->prev;
	LTNode* newnode = BuyTNode(x);
	prev->next = newnode;
	newnode->prev = prev;
	newnode->next = pos;
	pos->prev = newnode;
}

 

pos位置删除 

void LTDelete(LTNode* pos)
{
	assert(pos);
	LTNode* posPrev = pos->prev;
	LTNode* posNext = pos->next;
	posPrev->next = posNext;
	posNext->prev = posPrev;
	free(pos);
}

 销毁

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

 定义写完了之后，当然是测试我们的代码是否正确

test1：检验尾插和尾删

void TEST1()
{
	LTNode* plist = Inital();
	BackInsert(plist, 1);
	BackInsert(plist, 2);
	BackInsert(plist, 3);
	BackInsert(plist, 4);
	Print(plist);

	BackDelete(plist);
	Print(plist);

	BackDelete(plist);
	Print(plist);

	BackDelete(plist);
	Print(plist);

	BackDelete(plist);
	Print(plist);

	Destroy(plist);
	plist = NULL;

}

 

test2：检验头插和头删 

void TEST2()
{
	LTNode* plist = Inital();
	FrontInsert(plist, 1);
	FrontInsert(plist, 2);
	FrontInsert(plist, 3);
	FrontInsert(plist, 4);
	Print(plist);

	FrontDelete(plist);
	Print(plist);
	
	FrontDelete(plist);
	Print(plist);

	FrontDelete(plist);
	Print(plist);

	FrontDelete(plist);
	Print(plist);

	Destroy(plist);
	plist = NULL;
}

test3：查找某数和在pos位置插入

void TEST3()
{
	LTNode* plist = Inital();
	FrontInsert(plist, 1);
	FrontInsert(plist, 2);
	FrontInsert(plist, 3);
	FrontInsert(plist, 4);
	Print(plist);

	LTNode* pos = Find(plist, 3);
	if (pos)
	{
		LTInsert(pos, 30);
	}
	Print(plist);

	Destroy(plist);
	plist = NULL;
}

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