题解 | #判断链表中是否有环#

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
 import java.util.*;
public class Solution {
    public boolean hasCycle(ListNode head) {
        Set set = new HashSet<ListNode>();
        while(head!=null){
            if(!set.add(head)){
                return true;
            }
            head=head.next;
        }
        return false;
    }
}