CSharp  Java  Python  Swift  GO  WPF  Ruby  Scala  F#  JavaScript  SQL  PHP  Angular  HTML
Q. Program to insert a new node at the beginning of the doubly linked list.ExplanationIn 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
SolutionPython#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 JAVApublic 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#
