Program to Delete a New Node From the Middle of the Doubly Linked List

Q. Program to delete a new node from the middle of the doubly linked list.

Explanation

In this program, we will create a doubly linked list and delete a node from the middle of the list. If the list is empty, display the message "List is empty". If the list is not empty, we will calculate the size of the list and then divide it by 2 to get the mid-point of the list. Current will point to head node. We will iterate through the list till mid?point is reached. Now current will point to the middle node. We delete middle node such that current's previous node will point to the current's next node.

Program to delete a new node from the middle of the doubly linked list

Consider the above example, mid-point of above list is 3. Iterate current from head to mid-point. Now, the current is pointing to mid node which needs to be deleted. In this case, node new is the middle node which needs to be deleted. New can be deleted by making node 2 (current's previous node) to point to node 3 (current's next node). Set current to null.

Algorithm

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.
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.
deleteFromMid() will delete a node from the middle of the list:
1. It first checks whether the head is null (empty list) then, it will return from the function as there is no node present in the list.
2. If the list is not empty, it will check whether the list has only one node.
3. If the list has more than one node then, it will calculate the size of the list. Divide the size by 2 and store it in variable mid.
4. Iterate through the list till current points to mid node of the list.
5. Connect current's previous node to current?s next node.
6. Delete the current node by setting it to null.
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.

Solution

Python

#Represent a node of doubly linked list
class Node:
    def __init__(self,data):
        self.data = data;
        self.previous = None;
        self.next = None;
        
class DeleteMid:
    #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;
        
    #deleteFromMid() will delete a node from middle of the list
    def deleteFromMid(self):
        #Checks whether list is empty
        if(self.head == None):
            return;
        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;
                
            #If middle node is head of the list
            if(current == self.head):
                self.head = current.next;
            #If middle node is tail of the list
            elif(current == self.tail):
                self.tail = self.tail.previous;
            else:
                current.previous.next = current.next;
                current.next.previous = current.previous;
            #Delete the middle node
            current = None;
        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 = DeleteMid();
#Add nodes to the list
dList.addNode(1);
dList.addNode(2);
dList.addNode(3);
dList.addNode(4);
dList.addNode(5);
 
#Printing original list
print("Original List: ");
dList.display();
while(dList.head != None):
    dList.deleteFromMid();
    #Printing updated list
    print("Updated List: ")
    dList.display();

Output:

Original List: 
1 2 3 4 5 
Updated List: 
1 2 4 5 
Updated List: 
1 4 5 
Updated List: 
1 5 
Updated List: 
5 
Updated List: 
List is empty

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++;
}
 
//deleteFromMid() will delete a node from middle of the list
void deleteFromMid() {
    //Checks whether list is empty
    if(head == NULL) {
        return;
    }
    else {
        //current will point to head
        struct node *current = head;
        
        //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;
        }
        
        //If middle node is head of the list
        if(current == head) {
            head = current->next;
        }
        //If middle node is tail of the list
        else if(current == tail) {
            tail = tail->previous;
        }
        else {
            current->previous->next = current->next;
            current->next->previous = current->previous;
        }
        //Delete the middle node
        current = NULL;
     }
    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);
    addNode(3);
    addNode(4);
    addNode(5);
    
    //Printing original list
    printf("Original List: \n");
    display();
    while(head != NULL) {
        deleteFromMid();
        //Printing updated list
        printf("Updated List: \n");
        display();
    }    
 
    return 0;
}

Output:

Original List: 
1 2 3 4 5 
Updated List: 
1 2 4 5 
Updated List: 
1 4 5 
Updated List: 
1 5 
Updated List: 
5 
Updated List: 
List is empty

JAVA

public class DeleteMid {
    
    //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++;
    }
    
    //deleteFromMid() will delete a node from middle of the list
    public void deleteFromMid() {
        //Checks whether list is empty
        if(head == null) {
            return;
        }
        else {
            //current will point to head
            Node current = head;
            
            //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;
            }
            
            //If middle node is head of the list
            if(current == head) {
                head = current.next;
            }
            //If middle node is tail of the list
            else if(current == tail) {
                tail = tail.previous;
            }
            else {
                current.previous.next = current.next;
                current.next.previous = current.previous;
            }
            //Delete the middle node
            current = null;
        }
        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) {
        
        DeleteMid dList = new DeleteMid();
        //Add nodes to the list
        dList.addNode(1);
        dList.addNode(2);
        dList.addNode(3);
        dList.addNode(4);
        dList.addNode(5);
        
        //Printing original list
        System.out.println("Original List: ");
        dList.display();
        while(dList.head != null) {
            dList.deleteFromMid();
            //Printing updated list
            System.out.println("Updated List: ");
            dList.display();
        }
    }
}

Output:

Original List: 
1 2 3 4 5 
Updated List: 
1 2 4 5 
Updated List: 
1 4 5 
Updated List: 
1 5 
Updated List: 
5 
Updated List: 
List is empty

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 DeleteMid<T>{
            public int size = 0;
            //Represent the head and tail of the doubly linked list
            public Node<T> head = null;             
             public 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++;
            }
    
            //deleteFromMid() will delete a node from middle of the list
            public void deleteFromMid() {
                //Checks whether list is empty
                if(head == null) {
                    return;
                }
                else {
                    //current will point to head
                    Node<T> current = head;
 
                    //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;
                    }
 
                    //If middle node is head of the list
                    if(current == head) {
                        head = current.next;
                    }
                    //If middle node is tail of the list
                    else if(current == tail) {
                        tail = tail.previous;
                    }
                    else {
                        current.previous.next = current.next;
                        current.next.previous = current.previous;
                    }
                    //Delete the middle node
                    current = null;
                }
                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()
        {
            DeleteMid<int> dList = new DeleteMid<int>();
            //Add nodes to the list
            dList.addNode(1);
            dList.addNode(2);
            dList.addNode(3);
            dList.addNode(4);
            dList.addNode(5);
 
            //Printing original list
            Console.WriteLine("Original List: ");
            dList.display();
            while(dList.head != null) {
                dList.deleteFromMid();
                //Printing updated list
                Console.WriteLine("Updated List: ");
                dList.display();
            }
        }    
    }
}

Output:

Original List: 
1 2 3 4 5 
Updated List: 
1 2 4 5 
Updated List: 
1 4 5 
Updated List: 
1 5 
Updated List: 
5 
Updated List: 
List is empty

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 DeleteMid{
    //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++;
    }
    
    //deleteFromMid() will delete a node from middle of the list
    function deleteFromMid() {
        //Checks whether list is empty
        if($this->head == NULL) {
            return;
        }
        else {
            //current will point to head
            $current = $this->head;
            
            //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;
            }
            
            //If middle node is head of the list
            if($current == $this->head) {
                $this->head = $current->next;
            }
            //If middle node is tail of the list
            else if($current == $this->tail) {
                $this->tail = $this->tail->previous;
            }
            else {
                $current->previous->next = $current->next;
                $current->next->previous = $current->previous;
            }
            //Delete the middle node
            $current = NULL;
        }
        $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 DeleteMid();
//Add nodes to the list
$dList->addNode(1);
$dList->addNode(2);
$dList->addNode(3);
$dList->addNode(4);
$dList->addNode(5);
 
//Printing original list
print("Original List: <br>");
$dList->display();
while($dList->head != NULL) {
    $dList->deleteFromMid();
    //Printing updated list
    print("Updated List: <br>");
    $dList->display();
}
?>
</body>
</html>

Output:

Original List: 
1 2 3 4 5 
Updated List: 
1 2 4 5 
Updated List: 
1 4 5 
Updated List: 
1 5 
Updated List: 
5 
Updated List: 
List is empty

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