判断单链表中是否有环

#define _CRT_SECURE_NO_DEPRECATE
#include <iostream>
#include <cstdio>
#include<cstdlib>
#include <time.h>
#define OK 1
#define ERROR 0
#define TRUE 1
#define FALSE 0
typedef int Status;//函数结果状态代码，如OK。
typedef int ElemType;

typedef struct Node
{
ElemType data;
struct Node *next;
}Node, *LinkList;

//初始化带头结点的空链表
Status InitList(LinkList *L)
{
*L = (LinkList)malloc(sizeof(Node));//让L指向刚生成的头结点

if (!(*L))
{
return ERROR;//存储分配失败
}
(*L)->next = NULL;//指针域为空
return OK;
}

//返回L中元素个数
int ListLength(LinkList L)
{
int i = 0;
LinkList p = L->next;//p指向第一个结点
while (p)
{
i++;
p = p->next;
}
return i;
}

//头插法建立有头结点的单链表
void CreateListhHead(LinkList *L, int n)
{
LinkList p;
int i;
srand(time(0));
*L = (LinkList)malloc(sizeof(Node));
(*L)->next = NULL;
for (i = 0; i < n; i++)
{
p = (LinkList)malloc(sizeof(Node));
p->data = rand() % 100 + 1;
p->next = (*L)->next;
(*L)->next = p;
}
}

//尾插法建立有头结点的单链表
void CreateListTail(LinkList *L, int n)
{
LinkList p, r;
int i;
srand(time(0));
*L = (LinkList)malloc(sizeof(Node));
r = *L;
for (i = 0; i < n; i++)
{
p = (Node*)malloc(sizeof(Node));
p->data = rand() % 100 + 1;
r->next = p;
r = p;
}
r->next = (*L)->next->next;
}

//比较步数的方法
int HasLoop1(LinkList L)
{
LinkList cur1 = L;//定义结点cur1
int pos1 = 0;//cur1步数为0
while (cur1)
{
LinkList cur2 = L;//定义结点cur2
int pos2 = 0;//cur2步数为0
while (cur2)
{
if (cur2 == cur1) //cur1 cur2在相同结点
{
if (pos1 == pos2)//步数一样
{
break;//没有环
}
//在相同结点，步数不同，代表有环
else
{
printf("环的位置在第%d个结点处\n\n", pos2);
return OK;
}
}
cur2 = cur2->next;//没有发现环，继续下一个结点
pos2++;
}
cur1 = cur1->next;//cur1向后一个节点
pos1++;
}
return 0;
}

//利用快慢指针法
int HasLoop2(LinkList L)
{
int step1 = 1;
int step2 = 2;
LinkList p = L;//定义慢指针
LinkList q = L;//定义快指针
while (p != NULL&&q != NULL&&q->next != NULL)
{
p = p->next;
if (q->next != NULL)
{
q = q->next->next;
}
printf("p:%d,q:%d \n", p->data, q->data);
if (p == q)
{
return OK;
}
}
return 0;
}

int main()
{
LinkList L;
Status i;
char opp = '5';
ElemType e;
int find;
int type;

i = InitList(&L);
printf("\n 1.尾插法创建有环链表\n 2.头插法创建无环链表\n 3.判断链表是否有环\n 0.退出 \n\n");
while (opp != '0')
{
scanf("%c", &opp);
switch (opp)
{
case'1':
CreateListTail(&L, 10);
printf("利用尾插法成功创建有环链表L\n");
printf("\n");
break;

case'2':
CreateListhHead(&L, 10);
printf("利用头插法成功创建无环链表\n");
printf("\n");
break;

case'3':
printf("方法一：\n\n");
if (HasLoop1(L))
{
printf("链表有环\n\n");
}
else
{
printf("链表无环\n\n");
}
printf("方法二：\n\n");
if (HasLoop2(L))
{
printf("链表有环\n\n");
}
else
{
printf("链表无环\n\n\n");
}
printf("\n\n");
break;
case'0':
exit(0);
}
}

}