判断链表中是否有环存在

struct  listtype
{
int data;
struct listtype * next;
}list;

int find_cicle(list *head)
{
list *pFast=head;
list *pSlow=head;
if (pFast==NULL)
{
return -1;
}
while(pFast && pFast->next)
{
pFast=pFast->next->next;
pSlow=pSlow->next;
if (pFast==pSlow)
{
return 1;
}
}
return 0
}