Program To Insert A New Node At The Beginning Of The Singly Linked List

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

Explanation

In this program, we will create a singly linked list and add a new node at the beginning of the list. To accomplish this task, we will store head to a temporary node temp. Make newly added node as the new head of the list. Then, add temp (old head) after new head.

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

Consider the above list; node 1 represents the head of the original list. Let node New be the new node which needs to be added at the beginning of the list. Node temp will point to head, i.e. 1. Make New as the new head of the list and add temp after new head such that node next to New will be 1.

Algorithm

Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
Create another class InsertStart which has two attributes: head and tail.
addAtStart() will add a new node to the beginning of the list:
1. It first checks, whether the head is equal to null which means the list is empty.
2. If the list is empty, both head and tail will point to a newly added node.
3. If the list is not empty then, create temporary node temp will point to head.
4. Add the new node as head of the list.
5. Temp which was pointing to the old head will be added after the new head.
display() will display the nodes present in the list:
1. Define a node current which will initially point to the head of the list.
2. Traverse through the list till current points to null.
3. Display each node by making current to point to node next to it in each iteration.

Solution

Python

#Represent a node of the singly linked list
class Node:
    def __init__(self,data):
        self.data = data;
        self.next = None;
        
class InsertStart:
    #Represent the head and tail of the singly linked list
    def __init__(self):
        self.head = None;
        self.tail = None;
        
    #addAtStart() will add a new node to the beginning of the list
    def addAtStart(self, data):
        #Create a new node
        newNode = Node(data);
        
        #Checks if the list is empty
        if(self.head == None):
            #If list is empty, both head and tail will point to new node
            self.head = newNode;
            self.tail = newNode;
        else:
            #Node temp will point to head
            temp = self.head;
            #newNode will become new head of the list
            self.head = newNode;
            #Node temp(previous head) will be added after new head
            self.head.next = temp;
            
    #display() will display all the nodes present in 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 nodes to the start of the list: ");
        while(current != None):
            #Prints each node by incrementing pointer
            print(current.data ),
            current = current.next;
       
 
sList = InsertStart();
 
#Adding 1 to the list
sList.addAtStart(1);
sList.display();
#Adding 2 to the list
sList.addAtStart(2);
sList.display();
#Adding 3 to the list
sList.addAtStart(3);
sList.display();
#Adding 4 to the list
sList.addAtStart(4);
sList.display();

Output:

Adding nodes to the start of the list: 
1 
Adding nodes to the start of the list: 
2 1 
Adding nodes to the start of the list: 
3 2 1 
Adding nodes to the start of the list: 
4 3 2 1

C

#include <stdio.h>
 
//Represent a node of the singly linked list
struct node{
    int data;
    struct node *next;
};    
 
//Represent the head and tail of the singly linked list
struct node *head, *tail = NULL;
 
//addAtStart() will add a new node to the beginning of the list
void addAtStart(int data) {
    //Create a new node
    struct node *newNode = (struct node*)malloc(sizeof(struct node));
    newNode->data = data;
    newNode->next = NULL;
    
    //Checks if the list is empty
    if(head == NULL) {
        //If list is empty, both head and tail will point to new node
        head = newNode;
        tail = newNode;
    }
    else {
        //Node temp will point to head
        struct node *temp = head;
        //newNode will become new head of the list
        head = newNode;
        //Node temp(previous head) will be added after new head
        head->next = temp;
    }
}
    
//display() will display all the nodes present in 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 nodes 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();
 
    return 0;
}

Output:

Adding nodes to the start of the list: 
1 
Adding nodes to the start of the list: 
2 1 
Adding nodes to the start of the list: 
3 2 1 
Adding nodes to the start of the list: 
4 3 2 1

JAVA

public class InsertStart {
    
    //Represent a node of the singly linked list
    class Node{
        int data;
        Node next;
        
        public Node(int data) {
            this.data = data;
            this.next = null;
        }
    }
 
    //Represent the head and tail of the singly linked list
    public Node head = null;
    public Node tail = null;
    
    //addAtStart() will add a new node to the beginning of the list
    public void addAtStart(int data) {
        //Create a new node
        Node newNode = new Node(data);
        
        //Checks if the list is empty
        if(head == null) {
            //If list is empty, both head and tail will point to new node
            head = newNode;
            tail = newNode;
        }
        else {
            //Node temp will point to head
            Node temp = head;
            //newNode will become new head of the list
            head = newNode;
            //Node temp(previous head) will be added after new head
            head.next = temp;
        }
    }
    
    //display() will display all the nodes present in 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 nodes to the start of the list: ");
        while(current != null) {
            //Prints each node by incrementing pointer
            System.out.print(current.data + " ");
            current = current.next;
        }
        System.out.println();
    }
    
    public static void main(String[] args) {
        
        InsertStart sList = new InsertStart();
        
        //Adding 1 to the list
        sList.addAtStart(1);
        sList.display();
        
        //Adding 2 to the list
        sList.addAtStart(2);
        sList.display();
        
        //Adding 3 to the list
        sList.addAtStart(3);
        sList.display();
        
        //Adding 4 to the list
        sList.addAtStart(4);
        sList.display();
    }
}

Output:

Adding nodes to the start of the list: 
1 
Adding nodes to the start of the list: 
2 1 
Adding nodes to the start of the list: 
3 2 1 
Adding nodes to the start of the list: 
4 3 2 1

C#

using System;
                    
public class CreateList
{
    //Represent a node of the singly linked list
    public class Node<T>{
        public T data;
        public Node<T> next;
        
        public Node(T value) {
            data = value;
            next = null;
        }
    }
        
    public class InsertStart<T>{
        //Represent the head and tail of the singly linked list
        public Node<T> head = null;             
         public Node<T> tail = null;
    
        //addAtStart() will add a new node to the beginning of the list
        public void addAtStart(T data) {
            //Create a new node
            Node<T> newNode = new Node<T>(data);
 
            //Checks if the list is empty
            if(head == null) {
                //If list is empty, both head and tail will point to new node
                head = newNode;
                tail = newNode;
            }
            else {
                //Node temp will point to head
                Node<T> temp = head;
                //newNode will become new head of the list
                head = newNode;
                //Node temp(previous head) will be added after new head
                head.next = temp;
            }
        }
 
        //display() will display all the nodes present in 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 nodes to the start of the list: ");
            while(current != null) {
                //Prints each node by incrementing pointer
                Console.Write(current.data + " ");
                current = current.next;
            }
            Console.WriteLine();
        }
    }
    
    public static void Main()
    {
        InsertStart<int> sList = new InsertStart<int>();
        
        //Adding 1 to the list
        sList.addAtStart(1);
        sList.display();
        
        //Adding 2 to the list
        sList.addAtStart(2);
        sList.display();
        
        //Adding 3 to the list
        sList.addAtStart(3);
        sList.display();
        
        //Adding 4 to the list
        sList.addAtStart(4);
        sList.display();    
    }
}

Output:

Adding nodes to the start of the list: 
1 
Adding nodes to the start of the list: 
2 1 
Adding nodes to the start of the list: 
3 2 1 
Adding nodes to the start of the list: 
4 3 2 1

PHP

<!DOCTYPE html>
<html>
<body>
<?php
//Represent a node of singly linked list
class Node{
    public $data;
    public $next;
    
    function __construct($data){
        $this->data = $data;
        $this->next = NULL;
    }
}
class InsertStart{
    //Represent the head and tail of the singly linked list
    public $head;
    public $tail;
    function __construct(){
        $this->head = NULL;
        $this->tail = NULL;
    }
    
    //addAtStart() will add a new node to the beginning of the list
    function addAtStart($data) {
        //Create a new node
        $newNode = new Node($data);
        
        //Checks if the list is empty
        if($this->head == null) {
            //If list is empty, both head and tail will point to new node
            $this->head = $newNode;
            $this->tail = $newNode;
        }
        else {
            //Node temp will point to head
            $temp = $this->head;
            //newNode will become new head of the list
            $this->head = $newNode;
            //Node temp(previous head) will be added after new head
            $this->head->next = $temp;
        }
    }
    
    //display() will display all the nodes present in the list
    function display() {
        //Node current will point to head
        $current = $this->head;
        
        if($this->head == NULL) {
            print("List is empty <br>");
            return;
        }
        print("Adding nodes to the start of the list: <br>");
        while($current != NULL) {
            //Prints each node by incrementing pointer
            print($current->data . " ");
            $current = $current->next;
        }
        print("<br>");
    }
}
    
$sList = new InsertStart();
        
//Adding 1 to the list
$sList->addAtStart(1);
$sList->display();
 
//Adding 2 to the list
$sList->addAtStart(2);
$sList->display();
 
//Adding 3 to the list
$sList->addAtStart(3);
$sList->display();
 
//Adding 4 to the list
$sList->addAtStart(4);
$sList->display();
?>
</body>
</html>

Output:

Adding nodes to the start of the list: 
1 
Adding nodes to the start of the list: 
2 1 
Adding nodes to the start of the list: 
3 2 1 
Adding nodes to the start of the list: 
4 3 2 1

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