public boolean hasCycle(ListNode head) {

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