Q:

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

belongs to collection: Doubly Linked List Programs

robaa
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2022-11-10
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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.

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

  1. 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.
  2. 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.
  3. 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.
  4. 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.

Input:

 

#Adding 1 to the list  

dList.addAtStart(1);  

#Adding 2 to the list  

dList.addAtStart(2);  

#Adding 3 to the list  

dList.addAtStart(3);  

#Adding 4 to the list  

dList.addAtStart(4);  

#Adding 5 to the list  

dList.addAtStart(5);  

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
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All Answers

robaa
2022-11-11
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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 empty\n");  
        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

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Doubly Linked List Programs
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