Question

solve this Q in java languege

Write a method that return DoublyLinkedList as reversed string

For example:

If the elements of a list is

1, 2, 3, 4, 5, 6

the reverse string should be

6, 5, 4, 3, 2, 1

implement reverse method

you have two steps:

1- you should start traversing from the last element of DoublyLinkedList (the previous of the trailer)

2- you should add the element inside each node to string don't forget the space in the string. and there is no comma after last element

the is codee:

class Main {
public static void main(String[] args) {
//test you implmentation
DoublyLinkedList<Integer> l=new DoublyLinkedList<Integer>();
l.addFirst(6);
l.addFirst(5);
l.addFirst(4);
l.addFirst(3);
l.addFirst(2);
l.addFirst(1);
  
System.out.print(l.reverse());
  

}
}

class DoublyLinkedList<E> {

//---------------- nested Node class ----------------
private static class Node<E> {

private E element; // reference to the element stored at this node
private Node<E> prev; // reference to the previous node in the list
private Node<E> next; // reference to the subsequent node in the list

public Node(E e, Node<E> p, Node<E> n) {
element = e;
prev = p;
next = n;
}

// public accessor methods
public E getElement() { return element; }
public Node<E> getPrev() { return prev; }
public Node<E> getNext() { return next; }

// Update methods
public void setPrev(Node<E> p) { prev = p; }
public void setNext(Node<E> n) { next = n; }
} //----------- end of nested Node class -----------

// instance variables of the DoublyLinkedList
private Node<E> header; // header sentinel
private Node<E> trailer; // trailer sentinel
private int size = 0; // number of elements in the list

public DoublyLinkedList() {
header = new Node<>(null, null, null); // create header
trailer = new Node<>(null, header, null); // trailer is preceded by header
header.setNext(trailer); // header is followed by trailer
}

// public accessor methods

public int size() { return size; }
public boolean isEmpty() { return size == 0; }

public E first() {
if (isEmpty()) return null;
return header.getNext().getElement(); // first element is beyond header
}

public E last() {
if (isEmpty()) return null;
return trailer.getPrev().getElement(); // last element is before trailer
}

// public update methods
  
public void addFirst(E e) {
addBetween(e, header, header.getNext()); // place just after the header
}

public void addLast(E e) {
addBetween(e, trailer.getPrev(), trailer); // place just before the trailer
}

// private update methods
private void addBetween(E e, Node<E> predecessor, Node<E> successor) {
// create and link a new node
Node<E> newest = new Node<>(e, predecessor, successor);
predecessor.setNext(newest);
successor.setPrev(newest);
size++;
}

public String reverse ()
{
String s="";
Node c= trailer.prev;
DoublyLinkedList D1= new DoublyLinkedList();
  
//taraverse the list starting from the last element to the first
  
//hint :instead of prinitng add the new element to the string i.e s=(previous content of s) +r.getElement() + ,
  } //note that there are no comma after last elment.
}
return s;
}
  

}
  
  
//----------- end of DoublyLinkedList class -----------

Answer 1

DoublyLinkedList.java

public class DoublyLinkedList <E>
{
//---------------- nested Node class ----------------
private static class Node<E>
{
private E element; // reference to the element stored at this node
private Node<E> prev; // reference to the previous node in the list
private Node<E> next; // reference to the subsequent node in the list

public Node(E e, Node<E> p, Node<E> n) {
element = e;
prev = p;
next = n;
}

// public accessor methods
public E getElement() { return element; }
public Node<E> getPrev() { return prev; }
public Node<E> getNext() { return next; }

// Update methods
public void setPrev(Node<E> p) { prev = p; }
public void setNext(Node<E> n) { next = n; }
} //----------- end of nested Node class -----------

// instance variables of the DoublyLinkedList
private Node<E> header; // header sentinel
private Node<E> trailer; // trailer sentinel
private int size = 0; // number of elements in the list

public DoublyLinkedList()
{
header = new Node<>(null, null, null); // create header
trailer = new Node<>(null, header, null); // trailer is preceded by header
header.setNext(trailer); // header is followed by trailer
}

// public accessor methods

public int size() { return size; }
public boolean isEmpty() { return size == 0; }

public E first() {
if (isEmpty()) return null;
return header.getNext().getElement(); // first element is beyond header
}

public E last()
{
if (isEmpty()) return null;
return trailer.getPrev().getElement(); // last element is before trailer
}

// public update methods
public void addFirst(E e) {
addBetween(e, header, header.getNext()); // place just after the header
}

public void addLast(E e) {
addBetween(e, trailer.getPrev(), trailer); // place just before the trailer
}

// private update methods
private void addBetween(E e, Node<E> predecessor, Node<E> successor) {
// create and link a new node
Node<E> newest = new Node<>(e, predecessor, successor);
predecessor.setNext(newest);
successor.setPrev(newest);
size++;
}

public String reverse ()
{
String s="";
Node c= trailer.prev;
DoublyLinkedList D1= new DoublyLinkedList();
while(c.prev.getPrev()!=null)
{
s+=c.getElement()+", ";
c=c.prev;
}
s+=c.getElement();
//taraverse the list starting from the last element to the first
  
//hint :instead of prinitng add the new element to the string i.e s=(previous content of s) +r.getElement() + ,
return s;
} //note that there are no comma after last elment.
}

  

  
  
//----------- end of DoublyLinkedList class -----------

Main.java

class Main
{
public static void main(String[] args) {
//test you implmentation
DoublyLinkedList<Integer> l=new DoublyLinkedList<Integer>();
l.addFirst(6);
l.addFirst(5);
l.addFirst(4);
l.addFirst(3);
l.addFirst(2);
l.addFirst(1);
  
System.out.println(l.reverse());
}
}

output

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