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) {
       Set<ListNode> listNodeSet = new HashSet<>();
       boolean res = false;
       while(head != null && !res){
           if(!listNodeSet.contains(head)){
              listNodeSet.add(head);
              head = head.next;
           } else res = true;
       }
       return res;
    }
}