题解 | #判断链表中是否有环#

import java.util.*;
/**
 * 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) {

     HashSet<ListNode> ht=new LinkedHashSet<>();


        while(head!=null){
            if(ht.contains(head)) return true;
            ht.add(head);
            
            head=head.next;
        }

        return false;
    }
}