Linked List Cycle II

Given a linked list, return the node where the cycle begins. If there is no cycle, return

null

.

Follow up:

Can you solve it without using extra space?

/**

* Definition for singly-linked list.

* class ListNode {

* int val;

* ListNode next;

* ListNode(int x) {

* val = x;

* next = null;

* }

* }

*/

public class Solution {

public ListNode detectCycle(ListNode head) {

if(head==null)return null;

ListNode slow=head;

ListNode fast=head;

do{

if(fast==null||fast.next==null)return null;

fast=fast.next.next;

slow=slow.next;

} while(fast!=slow);

slow=head;

while(slow.val!=Integer.MAX_VALUE){

//这样可以通过。。。投机？

slow.val=Integer.MAX_VALUE;

slow=slow.next;

}

return slow;

}

}