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Q. Program to create a doubly linked list of n nodes and display it in reverse order.ExplanationIn this program, we create a doubly linked list, then reverse the list by reversing the direction of the list and print out the nodes. Traverse through the list by swapping the previous pointer with next pointer of each node. Then, swap the position of head and tail node that is, head of the original list will become tail of new list and tail of the original list will become head of the new list. So, the reversed list will be: Algorithm
SolutionPython#Represent a node of doubly linked list class Node: def __init__(self,data): self.data = data; self.previous = None; self.next = None; class ReverseList: #Represent the head and tail of the doubly linked list def __init__(self): self.head = None; self.tail = None; #addNode() will add a node to the list def addNode(self, data): #Create a new node newNode = Node(data); #If list is empty if(self.head == None): #Both head and tail will point to newNode self.head = self.tail = newNode; #head's previous will point to None self.head.previous = None; #tail's next will point to None, as it is the last node of the list self.tail.next = None; else: #newNode will be added after tail such that tail's next will point to newNode self.tail.next = newNode; #newNode's previous will point to tail newNode.previous = self.tail; #newNode will become new tail self.tail = newNode; #As it is last node, tail's next will point to None self.tail.next = None; #reverse() will reverse the doubly linked list def reverse(self): #Node current will point to head current = self.head; #Swap the previous and next pointers of each node to reverse the direction of the list while(current != None): temp = current.next; current.next = current.previous; current.previous = temp; current = current.previous; #Swap the head and tail pointers. temp = self.head; self.head = self.tail; self.tail = temp; #display() will print out the elements of the list def display(self): #Node current will point to head current = self.head; if(self.head == None): print("List is empty"); return; while(current != None): #Prints each node by incrementing pointer. print(current.data), current = current.next; dList = ReverseList(); #Add nodes to the list dList.addNode(1); dList.addNode(2); dList.addNode(3); dList.addNode(4); dList.addNode(5); print("Original List: "); dList.display(); #Reverse the given list dList.reverse(); #Displays the reversed list print("\nReversed List: "); dList.display(); Output: Original List: 1 2 3 4 5 Reversed List: 5 4 3 2 1 C#include <stdio.h> //Represent a node of the doubly linked list struct node{ int data; struct node *previous; struct node *next; }; //Represent the head and tail of the doubly linked list struct node *head, *tail = NULL; //addNode() will add a node to the list void addNode(int data) { //Create a new node struct node *newNode = (struct node*)malloc(sizeof(struct node)); newNode>data = data; //If list is empty if(head == NULL) { //Both head and tail will point to newNode head = tail = newNode; //head's previous will point to NULL head>previous = NULL; //tail's next will point to NULL, as it is the last node of the list tail>next = NULL; } else { //newNode will be added after tail such that tail's next will point to newNode tail>next = newNode; //newNode's previous will point to tail newNode>previous = tail; //newNode will become new tail tail = newNode; //As it is last node, tail's next will point to NULL tail>next = NULL; } } //reverse() will reverse the doubly linked list void reverse() { //Node current will point to head struct node *current = head, *temp = NULL; //Swap the previous and next pointers of each node to reverse the direction of the list while(current != NULL) { temp = current>next; current>next = current>previous; current>previous = temp; current = current>previous; } //Swap the head and tail pointers. temp = head; head = tail; tail = temp; } //display() will print out the nodes of the list void display() { //Node current will point to head struct node *current = head; if(head == NULL) { printf("List is empty\n"); return; } while(current != NULL) { //Prints each node by incrementing pointer. printf("%d ", current>data); current = current>next; } } int main() { //Add nodes to the list addNode(1); addNode(2); addNode(3); addNode(4); addNode(5); printf("Original List: \n"); display(); //Reverse the given list reverse(); //Displays the reversed list printf("\nReversed List: \n"); display(); return 0; } Output: Original List: 1 2 3 4 5 Reversed List: 5 4 3 2 1 JAVApublic class ReverseList { //Represent a node of the doubly linked list class Node{ int data; Node previous; Node next; public Node(int data) { this.data = data; } } //Represent the head and tail of the doubly linked list Node head, tail = null; //addNode() will add a node to the list public void addNode(int data) { //Create a new node Node newNode = new Node(data); //If list is empty if(head == null) { //Both head and tail will point to newNode head = tail = newNode; //head's previous will point to null head.previous = null; //tail's next will point to null, as it is the last node of the list tail.next = null; } else { //newNode will be added after tail such that tail's next will point to newNode tail.next = newNode; //newNode's previous will point to tail newNode.previous = tail; //newNode will become new tail tail = newNode; //As it is last node, tail's next will point to null tail.next = null; } } //reverse() will reverse the doubly linked list public void reverse() { //Node current will point to head Node current = head, temp = null; //Swap the previous and next pointers of each node to reverse the direction of the list while(current != null) { temp = current.next; current.next = current.previous; current.previous = temp; current = current.previous; } //Swap the head and tail pointers. temp = head; head = tail; tail = temp; } //display() will print out the elements of the list public void display() { //Node current will point to head Node current = head; if(head == null) { System.out.println("List is empty"); return; } while(current != null) { //Prints each node by incrementing the pointer. System.out.print(current.data + " "); current = current.next; } } public static void main(String[] args) { ReverseList dList = new ReverseList(); //Add nodes to the list dList.addNode(1); dList.addNode(2); dList.addNode(3); dList.addNode(4); dList.addNode(5); System.out.println("Original List: "); dList.display(); //Reverse the given list dList.reverse(); //Displays the reversed list System.out.println("\nReversed List: "); dList.display(); } } Output: Original List: 1 2 3 4 5 Reversed List: 5 4 3 2 1 C#using System; namespace DoublyLinkedList { public class Program { //Represent a node of the doubly linked list public class Node<T>{ public T data; public Node<T> previous; public Node<T> next; public Node(T value) { data = value; } } public class ReverseList<T>{ //Represent the head and tail of the doubly linked list protected Node<T> head = null; protected Node<T> tail = null; //addNode() will add a node to the list public void addNode(T data) { //Create a new node Node<T> newNode = new Node<T>(data); //If list is empty if(head == null) { //Both head and tail will point to newNode head = tail = newNode; //head's previous will point to null head.previous = null; //tail's next will point to null, as it is the last node of the list tail.next = null; } else { //newNode will be added after tail such that tail's next will point to newNode tail.next = newNode; //newNode's previous will point to tail newNode.previous = tail; //newNode will become new tail tail = newNode; //As it is last node, tail's next will point to null tail.next = null; } } //reverse() will reverse the doubly linked list public void reverse() { //Node current will point to head Node<T> current = head, temp = null; //Swap the previous and next pointers of each node to reverse the direction of the list while(current != null) { temp = current.next; current.next = current.previous; current.previous = temp; current = current.previous; } //Swap the head and tail pointers. temp = head; head = tail; tail = temp; } //display() will print out the nodes of the list public void display() { //Node current will point to head Node<T> current = head; if(head == null) { Console.WriteLine("List is empty"); return; } while(current != null) { //Prints each node by incrementing the pointer. Console.Write(current.data + " "); current = current.next; } } } public static void Main() { ReverseList<int> dList = new ReverseList<int>(); //Add nodes to the list dList.addNode(1); dList.addNode(2); dList.addNode(3); dList.addNode(4); dList.addNode(5); Console.WriteLine("Original List: "); dList.display(); //Reverse the given list dList.reverse(); //Displays the reversed list Console.WriteLine("\nReversed List: "); dList.display(); } } } Output: Original List: 1 2 3 4 5 Reversed List: 5 4 3 2 1 PHP<!DOCTYPE html> <html> <body> <?php //Represent a node of doubly linked list class Node{ public $data; public $previous; public $next; function __construct($data){ $this>data = $data; } } class ReverseList{ //Represent the head and tail of the doubly linked list public $head; public $tail; function __construct(){ $this>head = NULL; $this>tail = NULL; } //addNode() will add a node to the list function addNode($data){ //Create a new node $newNode = new Node($data); //If list is empty if($this>head == NULL) { //Both head and tail will point to newNode $this>head = $this>tail = $newNode; //head's previous will point to NULL $this>head>previous = NULL; //tail's next will point to NULL, as it is the last node of the list $this>tail>next = NULL; } else { //newNode will be added after tail such that tail's next will point to newNode $this>tail>next = $newNode; //newNode's previous will point to tail $newNode>previous = $this>tail; //newNode will become new tail $this>tail = $newNode; //As it is last node, tail's next will point to NULL $this>tail>next = NULL; } } //reverse() will reverse the doubly linked list function reverse() { //Node current will point to head $current = $this>head; //Swap the previous and next pointers of each node to reverse the direction of the list while($current != NULL) { $temp = $current>next; $current>next = $current>previous; $current>previous = $temp; $current = $current>previous; } //Swap the head and tail pointers. $temp = $this>head; $this>head = $this>tail; $this>tail = $temp; } //display() will print out the nodes of the list function display() { //Node current will point to head $current = $this>head; if($this>head == NULL) { print("List is empty <br>"); return; } while($current != NULL) { //Prints each node by incrementing pointer. print($current>data . " "); $current = $current>next; } } } $dList = new ReverseList(); //Add nodes to the list $dList>addNode(1); $dList>addNode(2); $dList>addNode(3); $dList>addNode(4); $dList>addNode(5); print("Original List: <br>"); $dList>display(); //Reverse the given list $dList>reverse(); //Displays the reversed list print("<br>Reversed List: <br>"); $dList>display(); ?> </body> </html> Output: Original List: 1 2 3 4 5 Reversed List: 5 4 3 2 1
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