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;
 *     }
 * }
 */
//用HashSet中不允许含有重复对象进行判断
public class Solution {
    public boolean hasCycle(ListNode head) {
        HashSet<ListNode> set = new HashSet<>();
        ListNode cur=head;
        while(cur!=null)
        {
            if(set.contains(cur)) return true;
            else{
                set.add(cur);
            }
            cur=cur.next;
        }
        return false;
        
    }
}