//
//
// dlist.h 
//	Data structure to manage doubly linked lists of integers.
//

#ifndef DLIST_H
#define DLIST_H

// The links and values are declared locally in dlist.cc and are used
// only within Dlist.
//
class Dlink; 


class Dlist {
  public:
    Dlist();
    // Construct a new empty list.

    ~Dlist();
    // Destructor for the list.  It deallocates the list, and all items on list

    int First() const;
    // Returns the first value in the list.

    int Last() const;
    // Returns the last value in the list.

    void Prepend(int value);
    // Adds value to beginning of list.

    void Append(int value);
    // Adds value to end of list

    bool InsertAfter(int newValue, int existingValue);
    // Adds newValue after the first occurrence of existingValue in
    // the list.  Returns false if existingValue is not in the list.
    // Otherwise it returns true.

    bool Remove(int value);
    // Removes value from the list.  Returns false if value is not in
    // the list.  Otherwise it returns true.
  
    void Clear ();
    // Removes all the elements from the list.  Frees the memory used
    // by each cell, but does not free the list itself.

    void Sort();
    // Sorts the list.

    void Print() const;
    // Prints the contents of the list to standard output.

    void SelfTest(int start);
    // Tests the list.  Start is the first value inserted in the list.

  private:
    Dlink *first;
    // Head of the list. NULL if list is empty

    Dlink *last;
    // Last element of list.  NULL if list is empty.

    Dlink *Find ( int value );
    // Return the cell in the list that contains value.  Return NULL
    // if value is not found.

    void Sort(Dlink *first, Dlink *last);
    // Internal Sort routine to sort a portion of the list.

    Dlink* Partition(Dlink *first, Dlink *last);
    // Internal routine used to partition the list for sorting using
    // the quicksort algorithm.
};

#endif // DLIST_H