Q:

Program to insert a new node at the middle of 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 create a doubly linked list and insert a new node in the middle of list. If list is empty, both head and tail will point to new node. If list is not empty, then we will calculate the size of the list and divide it by 2 to get the mid-point of the list where new node needs to be inserted.

Consider the above diagram; a new node needs to be added to the middle of the list. First, we calculate the size which in this case is 4. So, to get the mid-point, we divide it by 2 and store it in a variable mid. Node current will point to head. First, we iterate through the list until 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

  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 the doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
  3. addNode() will add node to 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, the new node will be inserted at the end of the list such that new node's previous pointer will point to tail.
    5. The new node will become the new tail. Tail's next pointer will point to null.
  4. addInMid() will add a node to the middle of the list:
    1. It first checks whether the head is null (empty list), then it will insert the node as the head.
    2. Both head and tail will point to a newly added node.
    3. If the list is not empty, then we calculate size and divide it by 2 to get the mid-point.
    4. Define node current that will point to head and 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.
  5. 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:

 

#Add nodes to the list  

dList.addNode(1);  

dList.addNode(2);  

#Adding node '3' in the middle  

dList.addInMid(3);  

#Adding node '4' in the middle  

dList.addInMid(4);  

#Adding node '5' in the middle  

dList.addInMid(5);  

Output:

Original list: 1 2 
Updated List: 1 3 2 
Updated List: 1 3 4 2 
Updated List: 1 3 5 4 2
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robaa
2022-11-10
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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 InsertMid:  
    #Represent the head and tail of the doubly linked list  
    def __init__(self):  
        self.head = None;  
        self.tail = None;  
        self.size = 0;  
          
    #addNode() will add a node to the list  
    def addNode(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;  
        else:  
            #newNode will be added after tail such that tail's next will point to newNode  
            self.tail.next = newNode;  
            #newNode's previous will point to tail  
            newNode.previous = self.tail;  
            #newNode will become new tail  
            self.tail = newNode;  
            #As it is last node, tail's next will point to None  
            self.tail.next = None;  
        #Size will count the number of nodes present in the list  
        self.size = self.size + 1;  
          
    #addInMid() will add a node to the middle of the list  
    def addInMid(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 point to None, as it is the last node of the list  
            self.tail.next = None;  
        else:  
            #current will point to head  
            current = self.head;  
              
            #Store the mid position of the list  
            mid = (self.size//2) if(self.size % 2 == 0)  else ((self.size+1)//2);  
              
            #Iterate through list till current points to mid position  
            for i in range(1, mid):  
                current = current.next;  
                  
            #Node temp will point to node next to current  
            temp = current.next;  
            temp.previous = current;  
              
            #newNode will be added between current and temp  
            current.next = newNode;  
            newNode.previous = current;  
            newNode.next = temp;  
            temp.previous = newNode;  
        self.size = self.size + 1;  
              
    #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;  
        while(current != None):  
            #Prints each node by incrementing pointer.  
            print(current.data),  
            current = current.next;  
              
        print();  
          
dList = InsertMid();  
#Add nodes to the list  
dList.addNode(1);  
dList.addNode(2);  
   
print("Original list: ");  
dList.display();  
   
#Adding node '3' in the middle  
dList.addInMid(3);  
print( "Updated List: ");  
dList.display();  
   
#Adding node '4' in the middle  
dList.addInMid(4);  
print("Updated List: ");  
dList.display();  
   
#Adding node '5' in the middle  
dList.addInMid(5);  
print("Updated List: ");  
dList.display();

 

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

 

C

#include <stdio.h>  
   
//Represent a node of the doubly linked list  
  
struct node{  
    int data;  
    struct node *previous;  
    struct node *next;  
};      
   
int size = 0;  
//Represent the head and tail of the doubly linked list  
struct node *head, *tail = NULL;  
   
//addNode() will add a node to the list  
void addNode(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;  
    }  
    else {  
        //newNode will be added after tail such that tail's next will point to newNode  
        tail->next = newNode;  
        //newNode's previous will point to tail  
        newNode->previous = tail;  
        //newNode will become new tail  
        tail = newNode;  
        //As it is last node, tail's next will point to NULL  
        tail->next = NULL;  
    }  
    //Size will count the number of nodes present in the list  
    size++;  
}  
   
//addInMid() will add a node to 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;  
      
    //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 point to NULL, as it is the last node of the list  
        tail->next = NULL;  
    }  
    else {  
        //current will point to head  
        struct node *current = head, *temp = NULL;  
          
        //Store the mid position of the list  
        int mid = (size % 2 == 0) ? (size/2) : ((size+1)/2);      
          
        //Iterate through list till current points to mid position  
        for(int i = 1; i < mid; i++){  
            current = current->next;  
        }  
          
        //Node temp will point to node next to current  
        temp = current->next;  
        temp->previous = current;  
          
        //newNode will be added between current and temp  
        current->next = newNode;  
        newNode->previous = current;  
        newNode->next = temp;  
        temp->previous = newNode;  
    }  
    size++;  
}  
   
//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;  
    }  
    while(current != NULL) {  
        //Prints each node by incrementing pointer.  
        printf("%d ", current->data);  
        current = current->next;  
    }  
    printf("\n");  
}  
      
int main()  
{  
    //Add nodes to the list  
    addNode(1);  
    addNode(2);  
      
    printf("Original list: \n");  
    display();  
      
    //Adding node '3' in the middle  
    addInMid(3);  
    printf( "Updated List: \n");  
    display();  
      
    //Adding node '4' in the middle  
    addInMid(4);  
    printf("Updated List: \n");  
    display();  
      
    //Adding node '5' in the middle  
    addInMid(5);  
    printf("Updated List: \n");  
    display();  
   
    return 0;  
}

 

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

 

JAVA

public class InsertMid {  
      
    //Represent a node of the doubly linked list  
  
    class Node{  
        int data;  
        Node previous;  
        Node next;  
          
        public Node(int data) {  
            this.data = data;  
        }  
    }  
      
    public int size = 0;  
    //Represent the head and tail of the doubly linked list  
    Node head, tail = null;  
      
    //addNode() will add a node to the list  
    public void addNode(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;  
        }  
        else {  
            //newNode will be added after tail such that tail's next will point to newNode  
            tail.next = newNode;  
            //newNode's previous will point to tail  
            newNode.previous = tail;  
            //newNode will become new tail  
            tail = newNode;  
            //As it is last node, tail's next will point to null  
            tail.next = null;  
        }  
        //Size will count the number of nodes present in the list  
        size++;  
    }  
      
    //addInMid() will add a node to the middle of the list  
    public void addInMid(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 point to null, as it is the last node of the list  
            tail.next = null;  
        }  
        else {  
            //current will point to head  
            Node current = head, temp = null;  
              
            //Store the mid position of the list  
            int mid = (size % 2 == 0) ? (size/2) : ((size+1)/2);      
              
            //Iterate through list till current points to mid position  
            for(int i = 1; i < mid; i++){  
                current = current.next;  
            }  
              
            //Node temp will point to node next to current  
            temp = current.next;  
            temp.previous = current;  
              
            //newNode will be added between current and temp  
            current.next = newNode;  
            newNode.previous = current;  
            newNode.next = temp;  
            temp.previous = newNode;  
        }  
        size++;  
    }  
      
    //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;  
        }  
        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) {  
          
        InsertMid dList = new InsertMid();  
        //Add nodes to the list  
        dList.addNode(1);  
        dList.addNode(2);  
          
        System.out.println("Original list: ");  
        dList.display();  
          
        //Adding node '3' in the middle  
        dList.addInMid(3);  
        System.out.println( "Updated List: ");  
        dList.display();  
          
        //Adding node '4' in the middle  
        dList.addInMid(4);  
        System.out.println("Updated List: ");  
        dList.display();  
          
        //Adding node '5' in the middle  
        dList.addInMid(5);  
        System.out.println("Updated List: ");  
        dList.display();  
    }  
}

 

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

 

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 InsertMid<T>{  
            public int size = 0;  
            //Represent the head and tail of the doubly linked list  
            protected Node<T> head = null;               
             protected Node<T> tail = null;  
              
            //addNode() will add a node to the list  
            public void addNode(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;  
                }  
                else {  
                    //newNode will be added after tail such that tail's next will point to newNode  
                    tail.next = newNode;  
                    //newNode's previous will point to tail  
                    newNode.previous = tail;  
                    //newNode will become new tail  
                    tail = newNode;  
                    //As it is last node, tail's next will point to null  
                    tail.next = null;  
                }  
                //Size will count the number of nodes present in the list  
                size++;  
            }  
      
            //addInMid() will add a node to the middle of the list  
            public void addInMid(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 point to null, as it is the last node of the list  
                    tail.next = null;  
                }  
                else {  
                    //current will point to head  
                    Node<T> current = head, temp = null;  
   
                    //Store the mid position of the list  
                    int mid = (size % 2 == 0) ? (size/2) : ((size+1)/2);      
   
                    //Iterate through list till current points to mid position  
                    for(int i = 1; i < mid; i++){  
                        current = current.next;  
                    }  
   
                    //Node temp will point to node next to current  
                    temp = current.next;  
                    temp.previous = current;  
   
                    //newNode will be added between current and temp  
                    current.next = newNode;  
                    newNode.previous = current;  
                    newNode.next = temp;  
                    temp.previous = newNode;  
                }  
                size++;  
            }  
      
            //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;  
                }  
                while(current != null) {  
                    //Prints each node by incrementing the pointer.  
  
                    Console.Write(current.data + " ");  
                    current = current.next;  
                }  
                Console.WriteLine();  
            }  
        }  
          
        public static void Main()  
        {  
            InsertMid<int> dList = new InsertMid<int>();  
            //Add nodes to the list  
            dList.addNode(1);  
            dList.addNode(2);  
   
            Console.WriteLine("Original list: ");  
            dList.display();  
   
            //Adding node '3' in the middle  
            dList.addInMid(3);  
            Console.WriteLine( "Updated List: ");  
            dList.display();  
   
            //Adding node '4' in the middle  
            dList.addInMid(4);  
            Console.WriteLine("Updated List: ");  
            dList.display();  
   
            //Adding node '5' in the middle  
            dList.addInMid(5);  
            Console.WriteLine("Updated List: ");  
            dList.display();  
        }      
    }  
}

 

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

 

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 InsertMid{  
    //Represent the head and tail of the doubly linked list  
    public $head;  
    public $tail;  
    public $size;  
    function __construct(){  
        $this->head = NULL;  
        $this->tail = NULL;  
        $this->size = 0;  
    }  
      
    //addNode() will add a node to the list  
    function addNode($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;  
        }  
        else {  
            //newNode will be added after tail such that tail's next will point to newNode  
            $this->tail->next = $newNode;  
            //newNode's previous will point to tail  
            $newNode->previous = $this->tail;  
            //newNode will become new tail  
            $this->tail = $newNode;  
            //As it is last node, tail's next will point to NULL  
            $this->tail->next = NULL;  
        }  
        //Size will count the number of nodes present in the list  
        $this->size++;  
    }  
      
    //addInMid() will add a node to the middle of the list  
    function addInMid($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 point to NULL, as it is the last node of the list  
            $this->tail->next = NULL;  
        }  
        else {  
            //current will point to head  
            $current = $this->head;  
            $temp = NULL;  
              
            //Store the mid position of the list  
            $mid = ($this->size % 2 == 0) ? ($this->size/2) : (($this->size+1)/2);      
              
            //Iterate through list till current points to mid position  
            for($i = 1; $i < $mid; $i++){  
                $current = $current->next;  
            }  
              
            //Node temp will point to node next to current  
            $temp = $current->next;  
            $temp->previous = $current;  
              
            //newNode will be added between current and temp  
            $current->next = $newNode;  
            $newNode->previous = $current;  
            $newNode->next = $temp;  
            $temp->previous = $newNode;  
        }  
        $this->size++;  
    }  
      
    //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;  
        }  
        while($current != NULL) {  
            //Prints each node by incrementing pointer.  
            print($current->data . " ");  
            $current = $current->next;  
        }  
        print("<br>");  
    }  
}  
      
$dList = new InsertMid();  
//Add nodes to the list  
$dList->addNode(1);  
$dList->addNode(2);  
   
print("Original list: <br>");  
$dList->display();  
   
//Adding node '3' in the middle  
$dList->addInMid(3);  
print( "Updated List: <br>");  
$dList->display();  
   
//Adding node '4' in the middle  
$dList->addInMid(4);  
print("Updated List: <br>");  
$dList->display();  
   
//Adding node '5' in the middle  
$dList->addInMid(5);  
print("Updated List: <br>");  
$dList->display();  
?>  
</body>  
</html>

 

Output:

Original list: 
1 2 
Updated List: 
1 3 2 
Updated List: 
1 3 4 2 
Updated List: 
1 3 5 4 2

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Doubly Linked List Programs
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