141. Linked List Cycle java solutions

Given a linked list, determine if it has a cycle in it.

Follow up:
Can you solve it without using extra space?

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 1 /**
 2  * Definition for singly-linked list.
 3  * class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) {
 7  *         val = x;
 8  *         next = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     public boolean hasCycle(ListNode head) {
14         if(head == null || head.next == null || head.next.next == null) return false;
15         ListNode slow = head;
16         ListNode fast = head.next.next;
17         while(fast != null){
18             slow = slow.next;
19             ListNode tmp = fast.next;
20             if(tmp == null) return false;
21             fast = tmp.next;
22             if(slow == fast) return true;
23         }
24         return false;
25     }
26 }