public ListNode DetectCycle(ListNode head)
{
//有个快慢指针判断是否有环
ListNode fast = head;
ListNode slow = head;
while (fast != null && fast.next != null)
{
fast = fast.next.next;
slow = slow.next;
if (fast == slow)
{
break;
}
}
if (fast != slow)
{
return(null);
}
//x + y = n (y + z)
// n=1 x=z
//set fastpoint to head
//exsit cycle
fast = head;
while (fast != slow)
{
fast = fast.next;
slow = slow.next;
}
return(fast);
}
public ListNode(int x)
{
val = x;
next = null;
}