Delete all the even nodes from a Doubly Linked List

Given a doubly linked list containing N nodes, the task is to delete all the even nodes from the list.

Examples:

Input: Initial List = 15 <=> 16 <=> 6 <=> 7 <=> 17 
Output: Final List = 15 <=> 7 <=> 17
Explanation: 16 and 6 are even nodes. So we need to delete them.

Input: Initial List = 5 <=> 3 <=> 6 <=> 8 <=> 4 <=> 1 <=> 2 <=> 9 
Output: Final List = 5 <=> 3 <=> 1 <=> 9 

The idea is to traverse the nodes of the doubly linked list one by one and get the pointer of the nodes having data even. Delete those nodes by following the approach used in this post.

Below is the implementation of above idea:  

C++

// C++ implementation to delete all
// the even nodes from the doubly
// linked list
#include <bits/stdc++.h>

using namespace std;

// Node of the doubly linked list
struct Node {
    int data;
    Node *prev, *next;
};

// function to insert a node at the beginning
// of the Doubly Linked List
void push(Node** head_ref, int new_data)
{
    // allocate node
    Node* new_node = new Node();

    // put in the data
    new_node->data = new_data;

    // since we are adding at the beginning,
    // prev is always NULL
    new_node->prev = NULL;

    // link the old list of the new node
    new_node->next = (*head_ref);

    // change prev of head node to new node
    if ((*head_ref) != NULL)
        (*head_ref)->prev = new_node;

    // move the head to point to the new node
    (*head_ref) = new_node;
}

// function to delete a node in a Doubly Linked List.
// head_ref --> pointer to head node pointer.
// del --> pointer to node to be deleted
void deleteNode(Node** head_ref, Node* del)
{
    // base case
    if (*head_ref == NULL || del == NULL)
        return;

    // If node to be deleted is head node
    if (*head_ref == del)
        *head_ref = del->next;

    // Change next only if node to be
    // deleted is NOT the last node
    if (del->next != NULL)
        del->next->prev = del->prev;

    // Change prev only if node to be
    // deleted is NOT the first node
    if (del->prev != NULL)
        del->prev->next = del->next;

    // Finally, free the memory occupied by del
    free(del);

    return;
}

// function to delete all the even nodes
// from the doubly linked list
void deleteEvenNodes(Node** head_ref)
{
    Node* ptr = *head_ref;
    Node* next;

    while (ptr != NULL) {
        next = ptr->next;
        // if true, delete node 'ptr'
        if (ptr->data % 2 == 0)
            deleteNode(head_ref, ptr);
        ptr = next;
    }
}

// function to print nodes in a
// given doubly linked list
void printList(Node* head)
{
    while (head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
}

// Driver program
int main()
{
    // start with the empty list
    Node* head = NULL;

    // create the doubly linked list
    // 15 <-> 16 <-> 7 <-> 6 <-> 17
    push(&head, 17);
    push(&head, 6);
    push(&head, 7);
    push(&head, 16);
    push(&head, 15);

    cout << "Original List: ";
    printList(head);

    deleteEvenNodes(&head);

    cout << "\nModified List: ";
    printList(head);
}

Java

// Java implementation to delete all
// the even nodes from the doubly
// linked list
class GFG
{

// Node of the doubly linked list
static class Node
{
    int data;
    Node prev, next;
};

// function to insert a node at the beginning
// of the Doubly Linked List
static Node push(Node head_ref, int new_data)
{
    // allocate node
    Node new_node = new Node();

    // put in the data
    new_node.data = new_data;

    // since we are adding at the beginning,
    // prev is always null
    new_node.prev = null;

    // link the old list of the new node
    new_node.next = (head_ref);

    // change prev of head node to new node
    if ((head_ref) != null)
        (head_ref).prev = new_node;

    // move the head to point to the new node
    (head_ref) = new_node;
    return head_ref;
}

// function to delete a node in a Doubly Linked List.
// head_ref -. pointer to head node pointer.
// del -. pointer to node to be deleted
static Node deleteNode(Node head_ref, Node del)
{
    // base case
    if (head_ref == null || del == null)
        return null;

    // If node to be deleted is head node
    if (head_ref == del)
        head_ref = del.next;

    // Change next only if node to be
    // deleted is NOT the last node
    if (del.next != null)
        del.next.prev = del.prev;

    // Change prev only if node to be
    // deleted is NOT the first node
    if (del.prev != null)
        del.prev.next = del.next;


    return head_ref;
}

// function to delete all the even nodes
// from the doubly linked list
static Node deleteEvenNodes(Node head_ref)
{
    Node ptr = head_ref;
    Node next;

    while (ptr != null)
    {
        next = ptr.next;

        // if true, delete node 'ptr'
        if (ptr.data % 2 == 0)
            deleteNode(head_ref, ptr);
        ptr = next;
    }
    return head_ref;
}

// function to print nodes in a
// given doubly linked list
static void printList(Node head)
{
    while (head != null)
    {
        System.out.print( head.data + " ");
        head = head.next;
    }
}

// Driver code
public static void main(String args[])
{
    // start with the empty list
    Node head = null;

    // create the doubly linked list
    // 15 <. 16 <. 7 <. 6 <. 17
    head = push(head, 17);
    head = push(head, 6);
    head = push(head, 7);
    head = push(head, 16);
    head = push(head, 15);

    System.out.print("Original List: ");
    printList(head);

    head=deleteEvenNodes(head);

    System.out.print( "\nModified List: ");
    printList(head);
}
}

// This code is contributed by Arnab Kundu

Python3

# Python3 implementation to delete all
# the even nodes from the doubly
# linked list
import math

# Node of the doubly linked list
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

# function to insert a node at the beginning
# of the Doubly Linked List
def push(head_ref, new_data):

    # allocate node
    new_node = Node(new_data)

    # put in the data
    new_node.data = new_data

    # since we are adding at the beginning,
    # prev is always None
    new_node.prev = None

    # link the old list of the new node
    new_node.next = head_ref

    # change prev of head node to new node
    if (head_ref!= None):
        head_ref.prev = new_node

    # move the head to point to the new node
    head_ref = new_node
    return head_ref

# function to delete a node in a Doubly Linked List.
# head_ref --> pointer to head node pointer.
# del --> pointer to node to be deleted
def deleteNode(head_ref, delete):

    # base case
    if (head_ref == None or delete == None):
        return

    # If node to be deleted is head node
    if (head_ref == delete):
        head_ref = delete.next

    # Change next only if node to be
    # deleted is NOT the last node
    if (delete.next != None):
        delete.next.prev = delete.prev

    # Change prev only if node to be
    # deleted is NOT the first node
    if (delete.prev != None):
        delete.prev.next = delete.next

    # Finally, free the memory occupied by del
    return head_ref

# function to delete all the even nodes
# from the doubly linked list
def deleteEvenNodes(head_ref):
    ptr = head_ref
    next = None

    while (ptr != None):
        next = ptr.next

        # if true, delete node 'ptr'
        if (ptr.data % 2 == 0):
            deleteNode(head_ref, ptr)
        ptr = next

# function to print nodes in a
# given doubly linked list
def printList(head):
    while (head != None) :
        print(head.data, end = " ")
        head = head.next

# Driver Code
if __name__=='__main__':

    # start with the empty list
    head = None

    # create the doubly linked list
    # 15 <-> 16 <-> 7 <-> 6 <-> 17
    head = push(head, 17)
    head = push(head, 6)
    head = push(head, 7)
    head = push(head, 16)
    head = push(head, 15)

    print("Original List: ", end = "")
    printList(head)

    deleteEvenNodes(head)

    print("\nModified List: ", end = "")
    printList(head)

# This code is contributed by Srathore

C#

// C# implementation to delete all
// the even nodes from the doubly
// linked list
using System;

class GFG
{

// Node of the doubly linked list
public class Node
{
    public int data;
    public Node prev, next;
};

// function to insert a node at the beginning
// of the Doubly Linked List
static Node push(Node head_ref, int new_data)
{
    // allocate node
    Node new_node = new Node();

    // put in the data
    new_node.data = new_data;

    // since we are adding at the beginning,
    // prev is always null
    new_node.prev = null;

    // link the old list of the new node
    new_node.next = (head_ref);

    // change prev of head node to new node
    if ((head_ref) != null)
        (head_ref).prev = new_node;

    // move the head to point to the new node
    (head_ref) = new_node;
    return head_ref;
}

// function to delete a node in a Doubly Linked List.
// head_ref -. pointer to head node pointer.
// del -. pointer to node to be deleted
static Node deleteNode(Node head_ref, Node del)
{
    // base case
    if (head_ref == null || del == null)
        return null;

    // If node to be deleted is head node
    if (head_ref == del)
        head_ref = del.next;

    // Change next only if node to be
    // deleted is NOT the last node
    if (del.next != null)
        del.next.prev = del.prev;

    // Change prev only if node to be
    // deleted is NOT the first node
    if (del.prev != null)
        del.prev.next = del.next;


    return head_ref;
}

// function to delete all the even nodes
// from the doubly linked list
static Node deleteEvenNodes(Node head_ref)
{
    Node ptr = head_ref;
    Node next;

    while (ptr != null)
    {
        next = ptr.next;

        // if true, delete node 'ptr'
        if (ptr.data % 2 == 0)
            deleteNode(head_ref, ptr);
        ptr = next;
    }
    return head_ref;
}

// function to print nodes in a
// given doubly linked list
static void printList(Node head)
{
    while (head != null)
    {
        Console.Write( head.data + " ");
        head = head.next;
    }
}

// Driver code
public static void Main(String []args)
{
    // start with the empty list
    Node head = null;

    // create the doubly linked list
    // 15 <. 16 <. 7 <. 6 <. 17
    head = push(head, 17);
    head = push(head, 6);
    head = push(head, 7);
    head = push(head, 16);
    head = push(head, 15);

    Console.Write("Original List: ");
    printList(head);

    head=deleteEvenNodes(head);

    Console.Write( "\nModified List: ");
    printList(head);
}
}

/* This code is contributed by PrinciRaj1992 */

Javascript

<script>
// javascript implementation to delete all
// the even nodes from the doubly
// linked list


// Node of the doubly linked list
class Node {
    constructor(val) {
        this.data = val;
        this.prev = null;
        this.next = null;
    }
}
// function to insert a node at the beginning
// of the Doubly Linked List
function push(head_ref , new_data)
{
    // allocate node
    var new_node = new Node();

    // put in the data
    new_node.data = new_data;

    // since we are adding at the beginning,
    // prev is always null
    new_node.prev = null;

    // link the old list of the new node
    new_node.next = (head_ref);

    // change prev of head node to new node
    if ((head_ref) != null)
        (head_ref).prev = new_node;

    // move the head to point to the new node
    (head_ref) = new_node;
    return head_ref;
}

// function to delete a node in a Doubly Linked List.
// head_ref -. pointer to head node pointer.
// del -. pointer to node to be deleted
function deleteNode(head_ref,  del)
{
    // base case
    if (head_ref == null || del == null)
        return null;

    // If node to be deleted is head node
    if (head_ref == del)
        head_ref = del.next;

    // Change next only if node to be
    // deleted is NOT the last node
    if (del.next != null)
        del.next.prev = del.prev;

    // Change prev only if node to be
    // deleted is NOT the first node
    if (del.prev != null)
        del.prev.next = del.next;
        return head_ref;
}

// function to delete all the even nodes
// from the doubly linked list
function deleteEvenNodes(head_ref)
{
    var ptr = head_ref;
    var next;

    while (ptr != null)
    {
        next = ptr.next;

        // if true, delete node 'ptr'
        if (ptr.data % 2 == 0)
            deleteNode(head_ref, ptr);
        ptr = next;
    }
    return head_ref;
}

// function to print nodes in a
// given doubly linked list
function printList(head)
{
    while (head != null)
    {
        document.write( head.data + " ");
        head = head.next;
    }
}

// Driver code

    // start with the empty list
    var head = null;

    // create the doubly linked list
    // 15 <. 16 <. 7 <. 6 <. 17
    head = push(head, 17);
    head = push(head, 6);
    head = push(head, 7);
    head = push(head, 16);
    head = push(head, 15);

    document.write("Original List: ");
    printList(head);

    head=deleteEvenNodes(head);

    document.write( "<br/>Modified List: ");
    printList(head);
// This code contributed by Rajput-Ji
</script>

Output:

Original List: 15 16 7 6 17 
Modified List: 15 7 17

Time Complexity: O(N), where N is the total number of nodes.
Auxiliary Space: O(1)