public class Solution {

     public boolean hasCycle(ListNode head) {

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

         ListNode slower =head,faster = head;

         while(faster!=null && faster.next!=null){

             if(faster==slower) return true;

             faster = faster.next.next;

             slower = slower.next;

         }

         return false;

     }

 }