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 fast=head.next.next;
        ListNode slow=head;
        
        while(fast!=null&&fast.next!=null&&fast!=slow){
            fast=fast.next.next;
            slow=slow.next;
        }
        if(fast==null||fast.next==null){
            return false;
        }
        return true;
    }
}