Program To Delete A New Node From The Beginning Of The Singly Linked List

Program to delete a new node from the beginning of the singly linked list

Explanation

In this program, we will create a singly linked list and delete a node from the beginning of the list. To accomplish this task, we need to make the head pointer pointing to the immediate next of the initial node which will now become the new head node of the list.

Program to delete a new node from the beginning of the singly linked list

Consider the above example; Node was the head of the list. Make head to point to next node in the list. Now, node 1 will become the new head of the list. Thus, deleting the Node.

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 DeleteStart which has two attributes: head and tail.
addNode() will add a new node to the list:
1. Create a new node.
2. It first checks, whether the head is equal to null which means the list is empty.
3. If the list is empty, both head and tail will point to a newly added node.
4. If the list is not empty, the new node will be added to end of the list such that tail's next will point to a newly added node. This new node will become the new tail of the list.
deleteFromStart() will delete a node from the beginning of the list:
1. It first checks whether the head is null (empty list) then, display the message "List is empty" and return.
2. If the list is not empty, it will check whether the list has only one node.
3. If the list has only one node, it will set both head and tail to null.
4. If the list has more than one node then, the head will point to the next node in the list and delete the old head node.
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 DeleteStart:
    #Represent the head and tail of the singly linked list
    def __init__(self):
        self.head = None;
        self.tail = None;
        
    #addNode() will add a new node to the list
    def addNode(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:
            #newNode will be added after tail such that tail's next will point to newNode
            self.tail.next = newNode;
            #newNode will become new tail of the list
            self.tail = newNode;
            
    #deleteFromStart() will delete a node from the beginning of the list
    def deleteFromStart(self):
        
        #Checks if the list is empty
        if(self.head == None):
            printf("List is empty\n");
            return;
        else:
            #Checks whether the list contains only one node
            #If not, head will point to next node in the list and tail will point to new head.
            if(self.head != self.tail):
                self.head = self.head.next;
                #If the list contains only one node
                #then, it will remove it and both head and tail will point to None
            else:
                self.head = self.tail = None;
                
    #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;
        while(current != None):
            #Prints each node by incrementing pointer
            print(current.data, end=" ");
            current = current.next;
        print();
 
sList =  DeleteStart();
 
#Adds data to the list
sList.addNode(1);
sList.addNode(2);
sList.addNode(3);
sList.addNode(4);
#Printing original list
print("Original List: ");
sList.display();
 
while(sList.head != None):
    sList.deleteFromStart();
    #Printing updated list
    print("Updated List: ");
    sList.display();

Output:

 Original List: 
1 2 3 4 
Updated List: 
2 3 4 
Updated List: 
3 4 
Updated List: 
4 
Updated List: 
List is empty

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;
 
//addNode() will add a new node to the list
void addNode(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 {
        //newNode will be added after tail such that tail's next will point to newNode
        tail->next = newNode;
        //newNode will become new tail of the list
        tail = newNode;
    }
}
 
//deleteFromStart() will delete a node from the beginning of the list
void deleteFromStart() {
    
    //Checks if the list is empty
    if(head == NULL) {
        printf("List is empty \n");
        return;
    }
    else {
        //Checks whether the list contains only one node
        //If not, the head will point to next node in the list and tail will point to the new head.
        if(head != tail) {
            head = head->next;
        }
        //If the list contains only one node 
        //then, it will remove it and both head and tail will point to NULL
        else {
            head = tail = NULL;
        }
    }
}
    
//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;
    }
    while(current != NULL) {
        //Prints each node by incrementing pointer
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}
    
int main()
{
    //Adds data to the list
    addNode(1);
    addNode(2);
    addNode(3);
    addNode(4);
    
    //Printing original list
    printf("Original List: \n");
    display();
    
    while(head != NULL) {
        deleteFromStart();
        //Printing updated list
        printf("Updated List: \n");
        display();
    }
 
    return 0;
}

Output:

Original List: 
1 2 3 4 
Updated List: 
2 3 4 
Updated List: 
3 4 
Updated List: 
4 
Updated List: 
List is empty

JAVA

public class DeleteStart {
    
    //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;
    
    //addNode() will add a new node to the list
    public void addNode(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 {
            //newNode will be added after tail such that tail's next will point to newNode
            tail.next = newNode;
            //newNode will become new tail of the list
            tail = newNode;
        }
    }
    
    //deleteFromStart() will delete a node from the beginning of the list
    public void deleteFromStart() {
        
        //Checks if the list is empty
        if(head == null) {
            System.out.println("List is empty");
            return;
        }
        else {
            //Checks whether the list contains only one node
            //If not, the head will point to next node in the list and tail will point to the new head.
            if(head != tail) {
                head = head.next;
            }
            //If the list contains only one node 
            //then, it will remove it and both head and tail will point to null
            else {
                head = tail = null;
            }
        }
    }
        
    //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;
        }
        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) {
        
        DeleteStart sList = new DeleteStart();
        
        //Adds data to the list
        sList.addNode(1);
        sList.addNode(2);
        sList.addNode(3);
        sList.addNode(4);
        
        //Printing original list
        System.out.println("Original List: ");
        sList.display();
        
        while(sList.head != null) {
            sList.deleteFromStart();
            //Printing updated list
            System.out.println("Updated List: ");
            sList.display();
        }
    }
}

Output:

Original List: 
1 2 3 4 
Updated List: 
2 3 4 
Updated List: 
3 4 
Updated List: 
4 
Updated List: 
List is empty

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 DeleteStart<T>{
        //Represent the head and tail of the singly linked list
        public Node<T> head = null;             
         public Node<T> tail = null;
    
        //addNode() will add a new node to the list
        public void addNode(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 {
                //newNode will be added after tail such that tail's next will point to newNode
                tail.next = newNode;
                //newNode will become new tail of the list
                tail = newNode;
            }
        }
    
        //deleteFromStart() will delete a node from the beginning of the list
        public void deleteFromStart() {
 
            //Checks if the list is empty
            if(head == null) {
                Console.WriteLine("List is empty");
                return;
            }
            else {
                //Checks whether the list contains only one node
                //If not, the head will point to next node in the list and tail will point to the new head.
                if(head != tail) {
                    head = head.next;
                }
                //If the list contains only one node 
                //then, it will remove it and both head and tail will point to null
                else {
                    head = tail = null;
                }
            }
        }
        
        //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;
            }
            while(current != null) {
                //Prints each node by incrementing pointer
                Console.Write(current.data + " ");
                current = current.next;
            }
            Console.WriteLine();
        }
    }
    
    public static void Main()
    {
        DeleteStart<int> sList = new DeleteStart<int>();
        
        //Adds data to the list
        sList.addNode(1);
        sList.addNode(2);
        sList.addNode(3);
        sList.addNode(4);
        
        //Printing original list
        Console.WriteLine("Original List: ");
        sList.display();
        
        while(sList.head != null) {
            sList.deleteFromStart();
            //Printing updated list
            Console.WriteLine("Updated List: ");
            sList.display();
        }
    }
}

Output:

Original List: 
1 2 3 4 
Updated List: 
2 3 4 
Updated List: 
3 4 
Updated List: 
4 
Updated List: 
List is empty

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 DeleteStart{
    //Represent the head and tail of the singly linked list
    public $head;
    public $tail;
    function __construct(){
        $this->head = NULL;
        $this->tail = NULL;
    }
    
    //addNode() will add a new node to the list
    function addNode($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 {
            //newNode will be added after tail such that tail's next will point to newNode
            $this->tail->next = $newNode;
            //newNode will become new tail of the list
            $this->tail = $newNode;
        }
    }
    
    //deleteFromStart() will delete a node from the beginning of the list
    function deleteFromStart() {
        
        //Checks if the list is empty
        if($this->head == null) {
            print("List is empty <br>");
            return;
        }
        else {
            //Checks whether the list contains only one node
            //If not, head will point to next node in the list and tail will point to new head.
            if($this->head != $this->tail) {
                $this->head = $this->head->next;
            }
            //If the list contains only one node 
            //then, it will remove it and both head and tail will point to null
            else {
                $this->head = $this->tail = null;
            }
        }
    }
    
    //display() will display all the nodes present in the list
    function display() {
        //Node current will point to head
        $current = $this->head;
        
        if($this->head == NULL) {
            print("List is empty <br>");
            return;
        }
        while($current != NULL) {
            //Prints each node by incrementing pointer
            print($current->data . " ");
            $current = $current->next;
        }
        print("<br>");
    }
}
 
$sList = new DeleteStart();
        
//Adds data to the list
$sList->addNode(1);
$sList->addNode(2);
$sList->addNode(3);
$sList->addNode(4);
 
//Printing original list
print("Original List: <br>");
$sList->display();
 
while($sList->head != null) {
    $sList->deleteFromStart();
    //Printing updated list
    print("Updated List: <br>");
    $sList->display();
}
?>
</body>
</html>

Output:

 Original List: 
1 2 3 4 
Updated List: 
2 3 4 
Updated List: 
3 4 
Updated List: 
4 
Updated List: 
List is empty

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