带头双向循环链表的实现

双向循环的节点由三部分构成，prev指针指向链表前一个节点，next指针指向后一个节点，data区储存节点数据。

双向循环链表结构看起来复杂，但简化了链表的插入删除等各种操作。

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

ListNode* ListCreate()
{
	ListNode* head = (ListNode*)malloc(sizeof(ListNode));
	if (head == NULL)
		return NULL;
	head->next = head;
	head->prev = head;
	head->data = 0;
	return head;
}

void ListDestory(ListNode* pHead)
{
	assert(pHead);
	ListNode* p= pHead->next;
	while (p!=pHead)
	{
		pHead->next = p->next;
		free(p);
		p = pHead->next;
	}
	//删除头节点
	free(pHead);
	pHead=NULL;
}

void ListPushBack(ListNode* pHead, DataType x)
{
	assert(pHead);
	ListNode* p = pHead;
	ListNode* s = (ListNode*)malloc(sizeof(ListNode));
	if (s == NULL)
		return;
	s->data = x;
	s->prev = p->prev;
	s->next = p;
	p->prev->next = s;
	p->prev = s;
	
}

void ListPopFront(ListNode* pHead)
{
	ListNode* p = pHead->next;
	p->next->prev = pHead;
	pHead->next = p->next;
	free(p);
}

void ListPushBack(ListNode* pHead, DataType x)
{
	assert(pHead);
	ListNode* p = pHead->prev;//获取链表的尾节点
	ListNode* s = (ListNode*)malloc(sizeof(ListNode));
	if (s == NULL)
		return;
	s->data = x;
	s->prev = p;
	s->next = pHead;
	p->next = s;
	pHead->prev = s;	
}

void ListPopBack(ListNode* pHead)
{
	ListNode* p = pHead->prev;
	p->prev->next = pHead;
	pHead->prev = p->prev;
	free(p);

}

void ListInsert(ListNode* pos, DataType x)
{
	ListNode* s = (ListNode*)malloc(sizeof(ListNode));
	if (s == NULL)
		return;
	s->data = x;
	s->next = pos->next;
	s->prev = pos;
	pos->next->prev = s;
	pos->next = s;
	
}

void ListErase(ListNode* pos)
{
	assert(pos);
	ListNode* p = pos->next;
	pos->next = p->next;
	p->next->prev = pos;
	free(p);
}