class List {
private:

  class Node {
  public:
    int data;
    Node * next;
    Node (int data, Node *next) {
      Node::data = data; Node::next = next;
    }
  };

  Node *head;

  // private copy method used by copy constructor and operator=
  void copy (const List &otherList);

  // private deleteAll method used by destructor and operator=
  void deleteAll();

   // recursive sub-method to calculate the sum of values greater than n
   int subSumGreaterThan(int n, Node* subHead) const;

   // recursive sub-method to see if the list contains a value less than m.  
   bool subHasValueLessThan(int m, Node* subHead) const;

   // recursive sub-method to see if the list contains a node directly followed by a node containing
   // double the value of the first node.
   bool subHasDoubleValueAfter(Node* subHead) const;

public:

  // default contstructor: creates empty list
  List () { head = NULL; };

  // copy constructor
  List (const List &otherList);

  // destructor: destroys list
  ~List ();

  // outputs list contents to cout
  void outputList () const;

  // adds a value at the beginning of the list
  void insert (int value);

  // assigns one linked list to another
  List& operator= (const List &otherList);

   // Method sumGreaterThan(n) returns the sum of the values in the given list that are greater than n.  
   // Note that "greater than" refers to the contents (value) of the node *not* its position in the list.  
   // If there are no values greater than n, this method returns 0.
   // This method does *not* change the list.
   int sumGreaterThan(int n) const;

   // Method hasValueLessThan(m) returns true if the list contains a value less than m, false otherwise.  
   // Note that "less than" refers to the contents (value) of the node *not* its position in the list.  
   // If there are no values in the list, this method returns false.
   // This method does *not* change the list.
   bool hasValueLessThan(int m) const;

   // Method hasDoubleValueAfter() returns true if the list contains a node directly followed by a node containing
   // double the value of the first node, and false otherwise.
   // If there are no values in the list, this method returns false.
   // This method does *not* change the list.
   bool hasDoubleValueAfter() const;

};