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;
 *     }
 * }
 */
public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head ==null||head.next==null||head.next.next==null)
        {
            return false;
        }

        ListNode head1 = head.next;
        ListNode head2 = head.next.next;
        while(true){
             if(head2.next==null||head2.next.next==null)
            {
                return false;
            }
            if(head2==head1)
            {
                return true;
            }
            head1 = head1.next;
            head2 = head2.next.next;
        }
    }
}