#ifndef ALT_LINKED_DEQUE_H
#define ALT_LINKED_DEQUE_H

#include <cstddef>       // ensure that NULL is defined

/**
 * An implementation of a deque using a doubly-linked list WITHOUT sentinels.
 */
template <typename Object>
class AltLinkedDeque {

public:
    AltLinkedDeque();                   // construct empty deque
    int size() const;                   // number of items in deque
    bool empty() const;                 // is the deque empty?
    const Object& front() const;        // access the front element
    const Object& back() const;         // access the back element
    void push_front(const Object& e);   // add element to the front of the deque
    void push_back(const Object& e);    // add element to the back of the deque
    void pop_front();                   // remove the front item from the deque
    void pop_back();                    // remove the back item from the deque

    // housekeeping functions
    AltLinkedDeque(const AltLinkedDeque& other);
    ~AltLinkedDeque();
    AltLinkedDeque& operator=(const AltLinkedDeque& other);

protected:

    struct Node {                       
        Object elem;                    // element
        Node*  prev;                    // prev pointer
        Node*  next;                    // next pointer
        Node(const Object& e = Object(), Node* prv = NULL, Node* nxt = NULL)
            : elem(e), prev(prv), next(nxt) { }        // constructor
    };

private:
    // instance variables
    Node* head;                                 // node with first deque element
    Node* tail;                                 // node with last deque element
    int n;                                      // number of items in deque

    // utilities for housekeeping
    void removeAll();                           // utility for housekeeping
    void copyFrom(const AltLinkedDeque& other); // utility for housekeeping

};  // end of AltLinkedDeque class

#include "AltLinkedDeque.tcc"
#endif