Program to Insert a New Node at the Beginning of the Doubly Linked List

Q. Program to insert a new node at the beginning of the doubly linked list.

Explanation

In this program, we will create a doubly linked list and insert every new node at the beginning of the list. If the list is empty, then head and tail will point to the newly added node. If the list is not empty then, insert the new node at the beginning of the list such that the head’s previous will point to new node. Make new node as head of the list, and its previous will point to null.

Program to insert a new node at the beginning of the doubly linked list

Consider the above example. Initially, 1 was the head of the list. Now new will be inserted before node 1 such that node 1’s previous will point to new. Make new as the head of the list, and its previous will point to null.

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.
addAtStart() will add a node to the beginning of 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, head’s previous will point to new node.
5. Make new node as head of the list.
6. Since new node became head so its previous should point to null.
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 InsertStart:      #Represent the head and tail of the doubly linked list      def __init__(self):          self.head = None;          self.tail = None;                #addAtStart() will add a node to the starting of the list      def addAtStart(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;          #Add newNode as new head of the list          else:              #head’s previous node will be newNode              self.head.previous = newNode;              #newNode’s next node will be head              newNode.next = self.head;              #newNode’s previous will point to None              newNode.previous = None;              #newNode will become new head              self.head = newNode;                    #display() will print out the nodes of the list      def display(self):          #Node current will point to head          current = self.head;          if(self.head == None):              print(“List is empty”);              return;          print(“Adding a node to the start of the list: “);          while(current != None):              #Prints each node by incrementing pointer.              print(current.data),              current = current.next;                        print();            dList = InsertStart();     #Adding 1 to the list  dList.addAtStart(1);  dList.display();  #Adding 2 to the list  dList.addAtStart(2);  dList.display();  #Adding 3 to the list  dList.addAtStart(3);  dList.display();  #Adding 4 to the list  dList.addAtStart(4);  dList.display();  #Adding 5 to the list  dList.addAtStart(5);  dList.display();  

Output:

Adding a node to the start of the list:   1   Adding a node to the start of the list:   2 1   Adding a node to the start of the list:   3 2 1   Adding a node to the start of the list:   4 3 2 1   Adding a node to the start of the 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;     //addAtStart() will add a node to the starting of the list  void addAtStart(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;      }      //Add newNode as new head of the list      else {          //head’s previous node will be newNode          head->previous = newNode;          //newNode’s next node will be head          newNode->next = head;          //newNode’s previous will point to NULL          newNode->previous = NULL;          //newNode will become new head          head = newNode;      }  }     //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;      }      printf(“Adding a node to the start of the list: n”);      while(current != NULL) {          //Prints each node by incrementing pointer.          printf(“%d “, current->data);          current = current->next;      }      printf(“n”);  }     int main()  {      //Adding 1 to the list      addAtStart(1);      display();      //Adding 2 to the list      addAtStart(2);      display();      //Adding 3 to the list      addAtStart(3);      display();      //Adding 4 to the list      addAtStart(4);      display();      //Adding 5 to the list      addAtStart(5);      display();         return 0;  }  

Output:

Adding a node to the start of the list:   1   Adding a node to the start of the list:   2 1   Adding a node to the start of the list:   3 2 1   Adding a node to the start of the list:   4 3 2 1   Adding a node to the start of the list:   5 4 3 2 1

JAVA

  public class InsertStart {            //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;            //addAtStart() will add a node to the starting of the list      public void addAtStart(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;          }          //Add newNode as new head of the list          else {              //head’s previous node will be newNode              head.previous = newNode;              //newNode’s next node will be head              newNode.next = head;              //newNode’s previous will point to null              newNode.previous = null;              //newNode will become new head              head = newNode;          }      }            //display() will print out the nodes 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;          }          System.out.println(“Adding a node to the start of the list: “);          while(current != null) {              //Prints each node by incrementing the pointer.                System.out.print(current.data + ” “);              current = current.next;          }          System.out.println();      }            public static void main(String[] args) {                    InsertStart dList = new InsertStart();                    //Adding 1 to the list          dList.addAtStart(1);          dList.display();          //Adding 2 to the list          dList.addAtStart(2);          dList.display();          //Adding 3 to the list          dList.addAtStart(3);          dList.display();          //Adding 4 to the list          dList.addAtStart(4);          dList.display();          //Adding 5 to the list          dList.addAtStart(5);          dList.display();      }  }  

Output:

Adding a node to the start of the list:   1   Adding a node to the start of the list:   2 1   Adding a node to the start of the list:   3 2 1   Adding a node to the start of the list:   4 3 2 1   Adding a node to the start of the 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 InsertStart<T>{              //Represent the head and tail of the doubly linked list              protected Node<T> head = null;                            protected Node<T> tail = null;                            //addAtStart() will add a node to the starting of the list              public void addAtStart(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;                  }                  //Add newNode as new head of the list                  else {                      //head’s previous node will be newNode                      head.previous = newNode;                      //newNode’s next node will be head                      newNode.next = head;                      //newNode’s previous will point to null                      newNode.previous = null;                      //newNode will become new head                      head = newNode;                  }              }                    //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;                  }                  Console.WriteLine(“Adding a node to the start of the list: “);                  while(current != null) {                      //Prints each node by incrementing the pointer.                        Console.Write(current.data + ” “);                      current = current.next;                  }                  Console.WriteLine();              }          }                    public static void Main()          {              InsertStart<int> dList = new InsertStart<int>();                 //Adding 1 to the list              dList.addAtStart(1);              dList.display();              //Adding 2 to the list              dList.addAtStart(2);              dList.display();              //Adding 3 to the list              dList.addAtStart(3);              dList.display();              //Adding 4 to the list              dList.addAtStart(4);              dList.display();              //Adding 5 to the list              dList.addAtStart(5);              dList.display();          }          }  }  

Output:

Adding a node to the start of the list:   1   Adding a node to the start of the list:   2 1   Adding a node to the start of the list:   3 2 1   Adding a node to the start of the list:   4 3 2 1   Adding a node to the start of the 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 InsertStart{      //Represent the head and tail of the doubly linked list      public $head;      public $tail;      function __construct(){          $this->head = NULL;          $this->tail = NULL;      }            //addAtStart() will add a node to the starting of the list      function addAtStart($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;          }          //Add newNode as new head of the list          else {              //head’s previous node will be newNode              $this->head->previous = $newNode;              //newNode’s next node will be head              $newNode->next = $this->head;              //newNode’s previous will point to NULL              $newNode->previous = NULL;              //newNode will become new head              $this->head = $newNode;          }      }            //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;          }          print(“Adding a node to the start of the list: <br>”);          while($current != NULL) {              //Prints each node by incrementing pointer.              print($current->data . ” “);              $current = $current->next;          }          print(“<br>”);      }  }        $dList = new InsertStart();     //Adding 1 to the list  $dList->addAtStart(1);  $dList->display();  //Adding 2 to the list  $dList->addAtStart(2);  $dList->display();  //Adding 3 to the list  $dList->addAtStart(3);  $dList->display();  //Adding 4 to the list  $dList->addAtStart(4);  $dList->display();  //Adding 5 to the list  $dList->addAtStart(5);  $dList->display();  ?>  </body>  </html>  

Output:

Adding a node to the start of the list:   1   Adding a node to the start of the list:   2 1   Adding a node to the start of the list:   3 2 1   Adding a node to the start of the list:   4 3 2 1   Adding a node to the start of the list:   5 4 3 2 1

Next Topic#

Q. Program to insert a new node at the beginning of the doubly linked list.

Explanation

Algorithm

Solution

Python

C

JAVA

C#

PHP

Wind Energy

Basics of PyTorch

You may also like