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) {
        if(null==head||null==head.next){
            return false;
        }

        ListNode slow=head;
        ListNode fast=head;

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

        return false;
    }
}