数据结构——循环单链表

循环单链表是单链表的另一种形式，其结构特点链表中最后一个结点的指针域不再是结束标记，而是指向整个链表的第一个结点，从而使链表形成一个环。和单链表相同，循环链表也有带头结点结构和不带头结点结构两种，带头结点的循环单链表实现插入和删除操作较为方便。

循环单链表只是将单链表的尾结点的指针指向头结点，就直接书写代码，有一点需要主要的是在循环单链表中只有头结点时，将头结点的指针域不指向空，而是执行自己。

1、循环单链表的存储结构

typedef int ElemType;


typedef struct CycNode
{
	ElemType data;
	struct CycNode *next;
}CycNode;


typedef struct CycLinkList
{
	CycNode *head;
	int count;
}CycLinkList, *pCycLinkList;

2、循环单链表的初始化

void InitCycList(pCycLinkList list)
{
	assert(list != NULL);

	list->count = 0;
	list->head = NULL;
}

3、循环单链表的扩容

static CycNode *BuyNode(ElemType val, CycNode *next)
{
	CycNode *s = (CycNode *)malloc(sizeof(CycNode));
	assert(s != NULL);

	s->data = val;
	if (next != NULL)
	{
		s->next = next;
	}
	else
	{
		s->next = s;
	}

	return s;
}

4、循环单链表的插入

void InsertCycList(pCycLinkList list, ElemType val, int pos)
{
	if (list->head == NULL)
	{
		list->head = BuyNode(val, NULL);
		list->count++;
		return;
	}

	if (pos < 0 || pos > list->count)
	{
		printf("insert pos is error\n");
		return;
	}

	CycNode *p = list->head;

	int pos2 = pos != 0 ? pos : list->count;

	while (pos2 > 1)
	{
		p = p->next;
		pos2--;
	}



	CycNode *s = BuyNode(val, p->next);
	p->next = s;

	if (pos == 0)
	{
		list->head = s;
	}

	list->count++;
}

5、循环单链表的删除

void DeleteCycList(pCycLinkList list, int pos)
{
	assert(list != NULL && list->head != NULL);

	if (list->head->next == list->head)
	{
		free(list->head);
		list->head = NULL;
		list->count--;
		return;
	}

	if (pos < 1 || pos > list->count)
	{
		printf("delete pos is error\n");
		return;
	}

	CycNode *p = list->head;

	if (pos == 1)
	{
		while (p->next != list->head)
		{
			p = p->next;
		}

		list->head = list->head->next;
	}
	else
	{
		while (pos > 2)
		{
			p = p->next;
			pos--;
		}
	}

	CycNode *q = p->next;
	p->next = q->next;

	free(q);
	list->count--;
}

6、循环单链表的打印函数

void ShowCycList(pCycLinkList list)
{
	assert(list != NULL);
	if (list->head == NULL)
	{
		printf("list is empty\n");
		return;
	}

	CycNode *p = list->head;

	while (p->next != list->head)
	{
		printf("%d  ", p->data);
		p = p->next;
	}

	printf("%d  \n", p->data);
}