/**
* 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) {
ListNode slow = head;
ListNode fast = head;
if(head == null || head.next == null){
return null;
}
while(true){
if(fast == null || fast.next == null){
return null;
}
slow = slow.next;
fast = fast.next.next;
if(slow == fast) break;
}
fast = head;
while(slow!=fast){
slow=slow.next;
fast=fast.next;
}
return fast;
}
}
