题目

public class Solution {public ListNode detectCycle(ListNode head) {if (head == null || head.next == null) {return null;}ListNode slow = head, fast = head;while (fast != null && fast.next != null) {slow = slow.next;fast = fast.next.next;if (slow == fast) {break;}}if (slow != fast) {return null;}slow = head;while (slow != fast) {slow = slow.next;fast = fast.next;}return slow;}
}