链表---双向循环链表(带头节点)

          **双向带头链表相较单向链表：**
            逻辑性更强，但实现更容易

下面是测试该链表功能的结果的结果 ：
以下代码分为三部分:
1.函数声明：
2.函数实现：
3.测试部分：
注：函数实现内有对函数实现的部分分析.

#include
#include
#include

//双向带头节点链表
#define ListType int 

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

//初始化链表
void InitList(ListNode** pphead) ;
//创建节点
ListNode* BuyListNode(ListType x);
//打印双向链表
void ListPrint(ListNode* phead);
//尾插
void ListPushBack(ListNode* phead,ListType x);
//尾删
void ListPopBack(ListNode* phead);
//头插
void ListPushFront(ListNode* phead,ListType x);
//头删
void ListPopFront(ListNode* phead);
//查找数据
ListNode* FindNum(ListNode* phead,ListType x);
//在查找数前插入节点
void ListInsert(ListNode* pos, ListType x);
//删除查找数对应的节点
void ListErase(ListNode* phead);
//清空链表
void ListClear(ListNode* phead);
//销毁双向链表
void ListDestroy(ListNode** pphead);

--------------------------------------------------

//初始化双向链表--1.让头节点两个指针指向自己
void InitList(ListNode** pphead)
{
	*pphead = BuyListNode(0);
	(*pphead)->next = *pphead;
	(*pphead)->prev = *pphead;
}

//创建节点---- 1.赋值 2.置空两个指针
ListNode* BuyListNode(ListType x)
{
	ListNode* Node = (ListNode*)malloc(sizeof(ListNode));
	Node->data = x;
	Node->next = NULL;
	Node->prev = NULL;

	return Node;
}

//打印双向链表--- 1.从第二个节点开始，遍历链表,并打印值
void ListPrint(ListNode* phead)
{
	ListNode* cur = phead->next;
	//法一:(较冗余,但打印效果较好)
	/*if (cur == phead)
	{
		printf("该链表为空!\n");
		return;
	}
	printf(" phead <-> ");
	while (cur != phead)
	{
		printf(" [%d]  <-> ", cur->data);
		cur = cur->next;
	}
	printf("phead\n");*/

	//法二:
	while (cur != phead)
	{
		printf(" [%d]  <-> ", cur->data);
		cur = cur->next;
	}
	printf("\n");

}

//尾插
void ListPushBack(ListNode* phead,ListType x)
{
	assert(phead);
	
	ListNode* newNode = BuyListNode(x);
	ListNode* cur = phead->next;

	//找到尾节点方法一:(较为冗余)
	while (cur->next != phead)
	{
		cur = cur->next;
	}
	//找到尾节点方法二：
	ListNode* tail = phead->prev;

	//双向链表插入新元素需要修改四个指针的指向
	cur->next = newNode;
	newNode->prev = cur; //未加此处导致 尾删和删除查找数 发生bug 
	newNode->next = phead;
	phead->prev = newNode;
}

//尾删
void ListPopBack(ListNode* phead)
{
	ListNode*cur = phead->next;

	if (cur == phead)
	{
		printf("该链表已无元素可删!\n");
		return;
	}

	while (cur->next != phead)
	{
		cur = cur->next;
	}
	//尾删需先找到尾节点前一个节点 
	ListNode* curPrev = cur->prev;
	//让该节点next指向头节点
	curPrev->next = phead;
	//头节点prev指向更新后的尾节点
	phead->prev = curPrev;
	free(cur);
	cur = NULL;
}

//头插
void ListPushFront(ListNode* phead,ListType x)
{
	ListNode* newNode = BuyListNode(x);
	ListNode* cur = phead->next;

	//插入改变四个指针变量
	phead->next = newNode;
	newNode->next = cur;
	newNode->prev = phead;
	cur->prev = newNode;
}

//头删
void ListPopFront(ListNode* phead)
{
	ListNode* cur = phead->next;
	if (cur == phead)
	{
		printf("该链表已无元素可删!\n");
		return;
	}
	ListNode* curNext = cur->next;
	phead->next = curNext;
	curNext->prev = phead;
}

//查找数所在位置
ListNode* FindNum(ListNode*  phead, ListType x)
{
	assert(phead);
	ListNode* cur = phead->next;
	while (cur != phead)
	{
		if (cur->data == x)
		{
			return cur;
		}
		cur = cur->next;
	}
	return NULL;
}

//删除查找数的节点
void ListErase(ListNode* pos)
{
	assert(pos);

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

//在查找数前一个位置处插入元素
void ListInsert(ListNode* pos, ListType x)
{
	ListNode* newNode = BuyListNode(x);
	ListNode* posPrev = pos->prev;

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

//清空链表
void ListClear(ListNode* phead)
{
	assert(phead);

	ListNode* cur = phead->next;
	while (cur != phead)
	{
		ListNode* next = cur->next;
		free(cur);
		cur = next ;
	}

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

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

//销毁链表
void ListDestory(ListNode** pphead)
{
	assert(pphead);

	ListClear(*pphead);

	free(*pphead);
	*pphead = NULL;
}
-----------------------------------------

int main()
{
	ListNode* phead = NULL;

	printf("测试尾插与头插---------------------------------------------------------------------:\n");
	InitList(&phead);
	ListPushBack(phead, 1);
	ListPushBack(phead, 2);
	ListPushBack(phead, 3);
	ListPushFront(phead, 10);
	ListPushFront(phead, 11);
	ListPushFront(phead, 12);
	ListPrint(phead);
	printf("测试尾删与头删----------------------------------------------------------------------:\n");
	ListPopBack(phead);
	ListPopFront(phead);
	ListPrint(phead);
	printf("测试Findnum，并在其前插入一个数(insert)，删除找到的数(erase):-----------------------\n");
	ListNode* pos = FindNum(phead, 2);
	ListInsert(pos, 8);
	ListPrint(phead);
	ListNode* Pos = FindNum(phead, 8);
	ListErase(Pos);
	ListPrint(phead);
	printf("测试清空链表:-------------------------------------------------------------------------\n");
	ListClear(phead);
	ListPrint(phead);
	return 0;
}