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

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

Explanation

In this program, we will create a singly linked list and add a new node at the middle of the list. To accomplish this task, we will calculate the size of the list and divide it by 2 to get the mid-point of the list where the new node needs to be inserted.

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

Consider the above diagram; node 1 represents the head of the original list. Let node New is the new node which needs to be added at the middle of the list. First, we calculate size which in this case is 4. So, to get the mid-point, we divide it by 2 and store it in a variable count. Node current will point to head. First, we iterate through the list till current points to mid position. Define another node temp which point to node next to current. Insert the New node between current and temp.

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 InsertMid which has three attributes: head, tail, and size that keep tracks of a number of nodes present in the list.
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.
addInMid() will add a new node at the middle 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 calculate the size of the list and divide it by 2 to get mid-point of the list.
4. Define node current that will iterate through the list till current will point to mid node.
5. Define another node temp which will point to node next to current.
6. The new node will be inserted after current and before temp such that current will point to the new node and the new node will point to temp.
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 InsertMid:
    #Represent the head and tail of the singly linked list
    def __init__(self):
        self.head = None;
        self.tail = None;
        self.size = 0;
        
    #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;
        #Size will count the number of nodes present in the list
        self.size = self.size + 1;
        
    #This function will add the new node at the middle of the list.
    def addInMid(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 would point to new node
            self.head = newNode;
            self.tail = newNode;
        else:
            #Store the mid position of the list
            count = (self.size//2) if(self.size % 2 == 0) else ((self.size+1)//2);
            #Node temp will point to head
            temp = self.head;
            current = None;
            
            #Traverse through the list till the middle of the list is reached
            for i in range(0, count):
                #Node current will point to temp
                current = temp;
                #Node temp will point to node next to it.
                temp = temp.next;
            
            #current will point to new node
            current.next = newNode;
            #new node will point to temp
            newNode.next = temp;
        self.size = self.size + 1;
            
    #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)
            current = current.next;
        
 
sList = InsertMid();
        
#Adds data to the list
sList.addNode(1);
sList.addNode(2);
 
print("Original list: ");
sList.display();
 
#Inserting node '3' in the middle
sList.addInMid(3);
print( "Updated List: ");
sList.display();
 
#Inserting node '4' in the middle
sList.addInMid(4);
print("Updated List: ");
sList.display();

Output:

 Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2

C

#include <stdio.h>
 
//Represent a node of the singly linked list
struct node{
    int data;
    struct node *next;
};    
 
int size;
//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;
    }
    //Size will count the number of nodes present in the list
    size++;
}
 
//This function will add the new node at the middle of the list.
void addInMid(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 would point to new node
        head = newNode;
        tail = newNode;
    }
    else {
        struct node *temp, *current;
        //Store the mid position of the list
        int count = (size % 2 == 0) ? (size/2) : ((size+1)/2);
        //Node temp will point to head
        temp = head;
        current = NULL;
 
        //Traverse through the list till the middle of the list is reached
        for(int i = 0; i < count; i++) {
            //Node current will point to temp
            current = temp;
            //Node temp will point to node next to it.
            temp = temp->next;
        }
        
        //current will point to new node
        current->next = newNode;
        //new node will point to temp
        newNode->next = temp;
    }
    size++;
}
    
//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);
    
    printf("Original list: \n");
    display();
    
    //Inserting node '3' in the middle
    addInMid(3);
    printf( "Updated List: \n");
    display();
    
    //Inserting node '4' in the middle
    addInMid(4);
    printf("Updated List: \n");
    display();
    
    return 0;
}

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2

JAVA

public class InsertMid {
    
    //Represent a node of the singly linked list
    class Node{
        int data;
        Node next;
        
        public Node(int data) {
            this.data = data;
            this.next = null;
        }
    }
 
    public int size;
    //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;
        }
        //Size will count the number of nodes present in the list
        size++;
    }
    
    //This function will add the new node at the middle of the list.
    public void addInMid(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 would point to new node
            head = newNode;
            tail = newNode;
        }
        else {
            Node temp, current;
            //Store the mid position of the list
            int count = (size % 2 == 0) ? (size/2) : ((size+1)/2);
            //Node temp will point to head
            temp = head;
            current = null;
 
            //Traverse through the list till the middle of the list is reached
            for(int i = 0; i < count; i++) {
                //Node current will point to temp
                current = temp;
                //Node temp will point to node next to it.
                temp = temp.next;
            }
            
            //current will point to new node
            current.next = newNode;
            //new node will point to temp
            newNode.next = temp;
        }
        size++;
    }
    
    //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) {
        
        InsertMid sList = new InsertMid();
        
        //Adds data to the list
        sList.addNode(1);
        sList.addNode(2);
        
        System.out.println("Original list: ");
        sList.display();
        
        //Inserting node '3' in the middle
        sList.addInMid(3);
        System.out.println( "Updated List: ");
        sList.display();
        
        //Inserting node '4' in the middle
        sList.addInMid(4);
        System.out.println("Updated List: ");
        sList.display();
    }
}

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2

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 InsertMid<T>{
        public int size;
        //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;
            }
            //Size will count the number of nodes present in the list
            size++;
        }
 
        //This function will add the new node at the middle of the list.
        public void addInMid(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 would point to new node
                head = newNode;
                tail = newNode;
            }
            else {
                Node<T> temp, current;
                //Store the mid position of the list
                int count = (size % 2 == 0) ? (size/2) : ((size+1)/2);
                //Node temp will point to head
                temp = head;
                current = null;
 
                //Traverse through the list till the middle of the list is reached
                for(int i = 0; i < count; i++) {
                    //Node current will point to temp
                    current = temp;
                    //Node temp will point to node next to it.
                    temp = temp.next;
                }
 
                //current will point to new node
                current.next = newNode;
                //new node will point to temp
                newNode.next = temp;
            }
            size++;
        }
 
        //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()
    {
        InsertMid<int> sList = new InsertMid<int>();
        
        //Adds data to the list
        sList.addNode(1);
        sList.addNode(2);
        
        Console.WriteLine("Original list: ");
        sList.display();
        
        //Inserting node '3' in the middle
        sList.addInMid(3);
        Console.WriteLine( "Updated List: ");
        sList.display();
        
        //Inserting node '4' in the middle
        sList.addInMid(4);
        Console.WriteLine("Updated List: ");
        sList.display();
    }
}

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2

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 InsertMid{
    //Represent the head and tail of the singly linked list
    public $head;
    public $tail;
    function __construct(){
        $this->head = NULL;
        $this->tail = NULL;
        $this->size = 0;
    }
    
    //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;
        }
        //Size will count the number of nodes present in the list
        $this->size++;
    }
    
    //This function will add the new node at the middle of the list.
    function addInMid($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 would point to new node
            $this->head = $newNode;
            $this->tail = $newNode;
        }
        else {
            //Store the mid position of the list
            $count = ($this->size % 2 == 0) ? ($this->size/2) : (($this->size+1)/2);
            //Node temp will point to head
            $temp = $this->head;
            $current = null;
 
            //Traverse through the list till the middle of the list is reached
            for($i = 0; $i < $count; $i++) {
                //Node current will point to temp
                $current = $temp;
                //Node temp will point to node next to it.
                $temp = $temp->next;
            }
            
            //current will point to new node
            $current->next = $newNode;
            //new node will point to temp
            $newNode->next = $temp;
        }
        $this->size++;
    }
    
    //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 InsertMid();
 
//Adds data to the list
$sList->addNode(1);
$sList->addNode(2);
 
print("Original list: <br>");
$sList->display();
 
//Inserting node '3' in the middle
$sList->addInMid(3);
print( "Updated List: <br>");
$sList->display();
 
//Inserting node '4' in the middle
$sList->addInMid(4);
print("Updated List: <br>");
$sList->display();
?>
</body>
</html>

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2

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