template<typename ItemType>
class Queue {
  class Node {
    Node *nextNode;
    ItemType _item;
  public:
    Node(ItemType item, Node *next = nullptr) : nextNode(next), _item(item) { }
    ItemType item() const { return _item; }
    Node* next() { return nextNode; }
  } _front = nullptr, _back = nullptr;
public:
  bool empty() const { return _front == nullptr; }
  void add(ItemType it) {
    if ( _front == nullptr )
      _front = _back = new Node(it);
    else
      _back = new Node(it, _back);
  }
  ItemType take() {
    ItemType x = _front->item();
    delete _front;
    _front = _front->next();
    if ( _front == nullptr )
      _back = nullptr;
  }
};