双向循环链表

双向循环链表的时间复杂度除了查找，都为O(1)。

首先创建出结构体

typedef struct ListNode {
	struct ListNode *next;
	struct ListNode *prev;
	LTDataType data;
} ListNode;

LTDataType其实是int类型的别名，方便后期代码维护

typedef int LTDataType;

双向链表的内容:

1：初始化

2：销毁链表

3：头插

4：尾插

5：头删

6：尾删

7：查找

初始化

首先要写一个创建新节点的函数，将第一个节点设置为头节点

ListNode *CreNode(LTDataType x) {
	ListNode *newnode = (ListNode *)malloc(sizeof(ListNode));
	newnode->data = x;
	newnode->next = NULL;
	newnode->prev = NULL;

	return newnode;
}

然后将节点的prev和next指向自己，形成循环，循环链表相比于单向链表的好处在于可以更加容易找到尾节点，增删改的时间复杂度小于单项链表。

 

ListNode* ListInit()
{
	ListNode* phead = BuyListNode(0);
	phead->next = phead;
	phead->prev = phead;

	return phead;
}

这里也可以使用void ListInit(ListNode** phead)二级指针来进行初始化

头插

 

void ListPushFront(ListNode* phead, LTDataType x)
{
	assert(phead);

	ListNode* newnode = BuyListNode(x);
	newnode->next = phead->next;
	phead->next->prev = newnode;

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

头删

 

void ListPopFront(ListNode* phead)
{
	assert(phead->next != phead);

	ListNode* first = phead->next;
	ListNode* second = first->next;
	phead->next = second;
	second->prev = phead;

	free(first);
	first = NULL;
}

尾删

 

void ListPopBack(ListNode* phead)
{
	assert(phead->next != phead);

	ListNode* tail = phead->prev;
	ListNode* prev = tail->prev;

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

	free(tail);
	tail = NULL;
}

尾插

 

void ListPushBack(ListNode* phead, LTDataType x)
{
	assert(phead);

	ListNode* tail = phead->prev;
	ListNode* newnode = BuyListNode(x);

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

全部代码

#include 
#include 
#include 
//定义数据类型
typedef int LTDataType;
//创建链表结构体

typedef struct ListNode {
	struct ListNode *next;
	struct ListNode *prev;
	LTDataType data;
} ListNode;

//创建新节点
ListNode *CreNode(LTDataType x) {
	ListNode *newnode = (ListNode *)malloc(sizeof(ListNode));
	newnode->data = x;
	newnode->next = NULL;
	newnode->prev = NULL;

	return newnode;
}

ListNode *ListInit() {
	//初始化节点，全指向自己
	ListNode *phead = CreNode(0);
	phead->next = phead;
	phead->prev = phead;

	return phead;
}

//头插
void ListPushFront(ListNode *phead, LTDataType x) {
	assert(phead);
	ListNode *newnode = CreNode(x);
	newnode->next = phead->next;
	phead->next->prev = newnode;

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

//尾插
void ListPushBack(ListNode *phead, LTDataType x) {
	//创建新节点
	ListNode *newnode = CreNode(x);
	ListNode *cur = phead->prev;
	cur->next = newnode;
	newnode->prev = cur;
	phead->prev = newnode;
	newnode->next = phead;
}

//打印
void print(ListNode *phead) {
	ListNode *cur = phead->next;
	while (cur != phead) {
		printf("%d ", cur->data);
		cur = cur->next;
	}
	printf("\n");
}

//头删
void ListPopFront(ListNode *phead) {
	assert(phead->next != phead);

	ListNode *first = phead->next;
	ListNode *second = first->next;
	phead->next = second;
	second->prev = phead;

	free(first);
	first = NULL;
}

//尾删
void ListPopBack(ListNode *phead) {
	ListNode *cur = phead->prev;
	ListNode *last = cur->prev;
	last->next = phead;
	phead->prev = last;
	free(cur);
	cur = NULL;
}

ListNode *ListFind(ListNode *phead, LTDataType x) {
	ListNode *cur = phead->next;
	while (cur != phead) {
		if (cur->data == x) {
			return cur;
		}
		cur = cur->next;
	}
	return NULL;
}

// pos位置之前插入x
void ListInsert(ListNode *pos, LTDataType x) {
	ListNode *cur = pos->prev;
	ListNode *newnode = CreNode(x);
	cur->next = newnode;
	newnode->prev = cur;
	newnode->next = pos;
	pos->prev = newnode;
}

//删除pos位置的值
void ListErase(ListNode *pos) {
	ListNode *prev = pos->prev;
	ListNode *next = pos->next;
	prev->next = next;
	next->prev = prev;
	free(pos);
	pos = NULL;
}

//计算链表长度
void ListSize(ListNode *phead) {
	ListNode *tail = phead->next;
	int cnt = 0;
	while (tail != phead) {
		cnt++;
		tail = tail->next;
	}
	printf("链表的长度为:%d", cnt);
}

int main(void) {
	ListNode *phead = ListInit(); //初始化，创建链表头节点
	ListPushFront(phead, 1);
	ListPushFront(phead, 2);
	ListPushFront(phead, 3);
	print(phead);
	ListPushBack(phead, 4);
	ListPushBack(phead, 5);
	ListPushBack(phead, 6);
	print(phead);
	ListPopFront(phead);
	print(phead);
	ListPopBack(phead);
	print(phead);
	ListNode *pos = ListFind(phead, 5);
	ListInsert(pos, 30);
	print(phead);
	ListErase(pos);
	print(phead);
	ListSize(phead);

	return 0;
}