private void postorderNR(Node<Item> r){
			if (r == null){
				return;
			}
			
			while (r != null || !s.isEmpty()){
				
				while (r != null){
	
					s.push(r);
					if (r.hasLeft()){
						r = r.left;
					} else {
						r = r.right;
					}
				}
				
				if (!s.isEmpty()){
					r = s.pop().data;
					queue.enqueue(r.data);
				}	
				
				while (!s.isEmpty() && s.peek().right == r){
					r = s.pop().data;
					queue.enqueue(r.data);

				}
				
				if (!s.isEmpty()){
					r = s.peek().right;
				} else {
					r = null;
				}
			}
		}