/** * Definition for singly-linked list. * class ListNode { * int val; * ListNode next; * ListNode(int x) { * val = x; * next = null; * } * } */ public class Solution { public boolean hasCycle(ListNode head) { //双指针判断是否有环 ListNode p1 = head; ListNode p2 = head; while(p1 != null && p2 != null && p2.next != null){ p1 = p1.next; p2 = p2.next.next; if(p1 != null && p2 != null && p1.val == p2.val){ return true; } } return false; } }