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