链表 C实现

#include <stdio.h>
#include <stdlib.h>
//建立链表
struct Link* creat();
//打印链表中的值
void print_link(struct Link*);
//链表的逆转
void reverse(struct Link*);
//求链表的中间值
void middle(struct Link*);
//判断链表是否带环,如果有环，输出环的入口值
void is_ring(struct Link*);
//删除链表倒数第三个值
void del(struct Link*);

int num = 0;

struct Link
{
	char a;
	struct Link *next;
};

int main()
{
	struct Link *head = NULL;

	head = creat();
	del(head);
//	is_ring(head);
	//	reverse(head);
	print_link(head);
	printf("\n");
//	middle(head);
	//	printf("\n");
	//	printf("%d\n", num);
	system("pause");
	return 0;
}

struct Link* creat()
{
	struct Link *head = NULL;
	struct Link *p = NULL, *q = NULL;
	struct Link *r = NULL;
	char c;
	int n = 5;

	p = (struct Link *)malloc(sizeof(struct Link));
	head = p;
	q = p;
	q->next = NULL;

	scanf("%c", &c);
	while(c != '0')
	{
		p = (struct Link *)malloc(sizeof(struct Link));
		p->a = c;
		p->next = NULL;
		q->next = p;
		q = p;
	
		scanf("%c", &c);
	}

	//创建带环的链表。
/*	r = head;
	while (n--)
	{
		r = r->next;
	}
	q->next = r;
*/
	return head;
}
   
void is_ring(struct Link *head)
{
	struct Link *fast = NULL, *slow = NULL;
	int flag = 0;
	fast = head;
	slow = head;

	if (fast->next == NULL)
	{
		printf("此链表为空！\n");
		return;
	}

	while (fast->next != NULL)
	{
		if (flag == 0)
		{
			fast = fast->next->next;
		}
		else
		{
			fast = fast->next;
		}
	
		slow = slow->next;
		if (fast == slow)
		{
			if (flag == 1)
			{
				printf("%c\n", fast->a);
				return;
			}

			printf("此链表存在环…\n");
			fast = head;
			flag = 1;
		}
		else if (fast == NULL)
		{
			printf("此链表不存在环…");
			return;
		}
	}
	printf("此链表不存在环…");
}

void middle(struct Link *head)
{
	struct Link *p = NULL, *q = NULL;

	p = head;
	q = head;
	
	if (p->next == NULL)
	{
		printf("此链表为空！\n");
		return;
	}

	while (p->next != NULL)
	{
		p = p->next->next;
		q = q->next;
		if (p == NULL)
		{
			printf("%d\n", q->a);
			return;
		}
	}
	printf("%d %d\n", q->a, q->next->a);
}
	



void reverse(struct Link *head)
{
	struct Link *p, *q, *r;
	p = head->next;

	if (p == NULL || p->next == NULL)
	{
		return;
	}

	r = p->next;
	q = r->next;
	p->next = NULL;
	while(q != NULL)
	{
		r->next = p;
		p = r;
		r = q;
		q = q->next;
	}
	r->next = p;
	head->next = r;
}

void del(struct Link *head)
{
	struct Link *p = NULL, *q = NULL;
	struct Link *r = NULL;
	int n = 3;
	p = head;
	q = head;

	while (n--)
	{
		if (p->next != NULL)
		{
			p = p->next;
		}
		else
		{
			printf("此链表个数少与3…\n");
			return;
		}
	}

	while (p->next != NULL)
	{
		p = p->next;
		q = q->next;
	}

	r = q->next;
	q->next = r->next;
	printf("%c\n", r->a);
	free(r);

}

void print_link(struct Link *head)
{
	struct Link *p = NULL;
	p = head->next;
	
	while(p != NULL)
	{
		printf("%c",p->a);
		p = p->next;
		num++;
	}
	printf("\n字符总数为:%d\n", num);


}