Chapter 3, Problem 31C

Reimplementation of DoublyLinkedList class using only one sentinel node:

The doubly linked list is a linked data structure which contains the collection of sequentially data with two sentinel nodes such as “header” and “trailer”.

• If there is only one sentinel node, then the list is circularly linked using sentinel node.
• That is, header is sentinel node means, the next of the header is first node of list and previous node of header is last node of list.

Code for DoublyLinkedList class using only one sentinel node:

//Define the DoublyLinkedList class

public class DoublyLinkedList<E>

{

  //Declare only one sentinel node

private Node<E> header;

  //Declare and initialize the "size" variable

private int size = 0;

/*Define the Constructor to construct a new empty list. */

  public DoublyLinkedList()

  {

//Create header sentinel

header = new Node<>(null, null, null);

  }

//Define the size() method

  public int size()

  {

/*Returns the number of elements in the linked list. */

  return size;

  }

  //Define isEmpty() method

  public boolean isEmpty()

  {

  //Check whether the linked list is empty

  return size == 0;

  }

//Define first() method

  public E first()

  {

  //Check whether the list is empty

  if(isEmpty())

  //Return null

  return null;

//Returns the first element of the list

  return header.getNext().getElement();

  }

//Define last() method

  public E last( )

  {

  //Check whether the list is empty

  if(isEmpty())

  //Return null

  return null;

/*Returns the last element of the list using the single sentinel node "header". */

  return header.getPrev().getElement( );

  }

  //Define addFirst() method

  public void addFirst(E e)

  {

/*Call addBetween() method to adds element "e" to the front of the list. */

  addBetween(e, header, header.getNext

  }

  /Define the addLast() method

  public void addLast(E e)

  {

/*Call addBetween() method to adds element e to the end of the list using single sentinel node "header". */

  addBetween(e, header.getPrev(), header);

  }

//Define the removeFirst() method

  public E removeFirst()

  {

  //Check whether the list is empty

  if (isEmpty())

  //Return null

  return null;

/*Call remove() method to removes and returns the first element of the list. */

  return remove(header...