Program to Create a Doubly Linked List of N Nodes and Display it in Reverse Order

Q. Program to create a doubly linked list of n nodes and display it in reverse order.

Explanation

In this program, we create a doubly linked list, then reverse the list by reversing the direction of the list and print out the nodes.

Program to create a doubly linked list of n nodes and display it in reverse order

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:

Program to create a doubly linked list of n nodes and display it in reverse order

Algorithm

Define a Node class which represents a node in the list. It will have three properties: data, previous which will point to the previous node and next which will point to the next node.
Define another class for creating a doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
addNode() will add node to the list:
1. It first checks whether the head is null, then it will insert the node as the head.
2. Both head and tail will point to a newly added node.
3. Head’s previous pointer will point to null and tail’s next pointer will point to null.
4. If the head is not null, the new node will be inserted at the end of the list such that new node’s previous pointer will point to tail.
5. The new node will become the new tail. Tail’s next pointer will point to null.
reverse() will reverse the given doubly linked list.
1. Define a node current which will initially point to head.
2. Traverse through the list by making current to point to current.next in each iteration till current points to null.
3. In each iteration, swap previous and next pointer of each node to reverse the direction of the list.
4. In the end, swap the position of head and tail.
display() will show all the nodes present in the list.
1. Define a new node ‘current’ that will point to the head.
2. Print current.data till current points to null.
3. Current will point to the next node in the list in each iteration.

Solution

Python

  #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 emptyn”);          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

JAVA

  public 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

Next Topic#

Q. Program to create a doubly linked list of n nodes and display it in reverse order.

Explanation

Algorithm

Solution

Python

C

JAVA

C#

PHP

Potential Energy

Program to Find The Transpose of a Given Matrix

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