// Oldham, Jeffrey D.
// 2000Mar25
// CS1321

// Deque Implementation

// This class implements a deque, a Double-Ended QUEue.  ("Deque" is
// pronounced "deck.")  This data structure supports insertion and
// deletion at both the front and the back in a constant amount of
// time.  In contrast, vectors support constant-time insertion and
// deletion only at the back, i.e., right.

// We implement a deque using a doubly-linked list.

#include "dll.h"
#include <iostream>

class deque {
public:
  typedef dll::item_type item_type; // 0
  typedef unsigned long size_type; // 4
  // no need for a constructor

  // insertion routines
  void push_front(const item_type & i) {// 1
    lst.insert(lst.begin(), i);
    return;
  }
  void push_back(const item_type & i) {	// 1
    lst.insert(lst.end(), i);
    return;
  }

  // checking for empty		// 3
  bool empty(void) const { return lst.begin() == lst.end(); }

  // removal routines
  void pop_front(void) {	// 3
    if (!empty())
      lst.erase(lst.begin());
    return;
  }
  void pop_back(void) {		// 3
    if (!empty())
      lst.erase(lst.pred(lst.end()));
    return;
  }

  // access routines
  item_type& front(void) {	// 4
    if (!empty())
      return lst.begin()->itm;
    else
      throw "deque: front() on empty deque";
  }
  const item_type& front(void) const { // 4
    if (!empty())
      return lst.begin()->itm;
    else
      throw "deque: front() on empty deque";
  }
  item_type& back(void) {	// 4
    if (!empty())
      return lst.pred(lst.end())->itm;
    else
      throw "deque: back() on empty deque";
  }
  const item_type& back(void) const { // 4
    if (!empty())
      return lst.pred(lst.end())->itm;
    else
      throw "deque: back() on empty deque";
  }
  const item_type& operator[](size_type i) const { // 4
    dll::link * l;
    for (l = lst.begin();
	 l != lst.end() && i > 0;
	 l = lst.succ(l), i -= 1)
      ;
    if (i == 0 && l != lst.end())
      return l->itm;
    else
      throw "deque: illegal element access";
  }
  item_type& operator[](size_type i) { // 4
    dll::link * l;
    for (l = lst.begin();
	 l != lst.end() && i > 0;
	 l = lst.succ(l), i -= 1)
      ;
    if (i == 0 && l != lst.end())
      return l->itm;
    else
      throw "deque: illegal element access";
  }

  // output
  friend ostream& operator<<(ostream& out, const deque & dq) {// 2
    for (dll::link * l = dq.lst.begin(); l != dq.lst.end(); l = dq.lst.succ(l))
      out << l->itm;
    return out;
  }

private:
  dll lst;			// 0
};