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