Remove all the Even Digit Sum Nodes from a Doubly Linked List

Given a Doubly linked list containing N nodes, the task is to remove all the nodes from the list which contains elements whose digit sum is even.

Examples:

Input: DLL = 18 <=> 15 <=> 8 <=> 9 <=> 14 
Output: 18 <=> 9 <=> 14 
Explanation:
The linked list contains : 
18 -> 1 + 8 = 9 
15 -> 1 + 5 = 6 
8 -> 8 
9 -> 9 
14 -> 1 + 4 = 5 
Here, digit sum for nodes containing 15 and 8 are even. 
Hence, these nodes have been deleted.

Input: DLL = 5 <=> 3 <=> 4 <=> 2 <=> 9 
Output: 5 <=> 3 <=> 9 
Explanation:
The linked list contains two digit sum values 4 and 2. 
Hence, these nodes have been deleted. 

Approach:
A simple approach is to traverse the nodes of the doubly linked list one by one and for each node first, find the digit sum for the value present in the node by iterating through each digit and then finally remove the nodes whose digit sum is even.

Below is the implementation of the above approach: 

C++

// C++ implementation to remove all
// the Even Digit Sum Nodes from a
// 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 the node
    Node* new_node
        = (Node*)malloc(sizeof(struct Node));

    // Insert 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 off the new node
    new_node->next = (*head_ref);

    // Change the 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 find the digit sum
// for a number
int digitSum(int num)
{
    int sum = 0;
    while (num) {
        sum += (num % 10);
        num /= 10;
    }

    return sum;
}

// 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 the 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 to remove all
// the Even Digit Sum Nodes from a
// doubly linked list
void deleteEvenDigitSumNodes(Node** head_ref)
{
    Node* ptr = *head_ref;
    Node* next;

    // Iterating through the linked list
    while (ptr != NULL) {
        next = ptr->next;

        // If node's data's digit sum
        // is even
        if (!(digitSum(ptr->data) & 1))
            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 Code
int main()
{

    Node* head = NULL;

    // Create the doubly linked list
    // 18 <-> 15 <-> 8 <-> 9 <-> 14
    push(&head, 14);
    push(&head, 9);
    push(&head, 8);
    push(&head, 15);
    push(&head, 18);

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

    deleteEvenDigitSumNodes(&head);

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

Java

// Java implementation to
// remove all the Even
// Digit Sum Nodes from a
// doubly linked list
import java.util.*;
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 the node
  Node new_node = new Node();

  // Insert 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
  // off the new node
  new_node.next = head_ref;

  // Change the 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 find the digit sum
// for a number
static int digitSum(int num)
{
  int sum = 0;
  while (num > 0)
  {
    sum += (num % 10);
    num /= 10;
  }
  return sum;
}

// 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 head_ref;

  // If the 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
  del = null;

  return head_ref;
}

// Function to to remove all
// the Even Digit Sum Nodes from a
// doubly linked list
static Node deleteEvenDigitSumNodes(Node head_ref)
{
  Node ptr = head_ref;
  Node next;

  // Iterating through the linked list
  while (ptr != null)
  {
    next = ptr.next;

    // If node's data's digit sum
    // is even
    if (!(digitSum(ptr.data) % 2 == 1))
      head_ref = 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)
{
  Node head = null;

  // Create the doubly linked list
  // 18 <. 15 <. 8 <. 9 <. 14
  head = push(head, 14);
  head = push(head, 9);
  head = push(head, 8);
  head = push(head, 15);
  head = push(head, 18);

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

  head = deleteEvenDigitSumNodes(head);

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

// This code is contributed by shikhasingrajput

Python3

# Python3 implementation to remove all
# the Even Digit Sum Nodes from a
# doubly linked list

# Node of the doubly linked list
class Node():

    def __init__(self):

        self.data = 0
        self.prev = None
        self.next = None

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

    # Allocate the node
    new_node = Node()

    # Insert the data
    new_node.data = new_data

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

    # Link the old list off the new node
    new_node.next = head_ref

    # Change the 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 find the digit sum
# for a number
def digitSum(num):

    sum = 0

    while (num != 0):
        sum += (num % 10)
        num //= 10

    return sum

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

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

    # If the 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 delete
    del delete

    return

# Function to to remove all
# the Even Digit Sum Nodes from a
# doubly linked list
def deleteEvenDigitSumNodes(head_ref):

    ptr = head_ref
    next = None

    # Iterating through the linked list
    while (ptr != None):
        next = ptr.next

        # If node's data's digit sum
        # is even
        if (not (digitSum(ptr.data) & 1)):
            deleteNode(head_ref, ptr)

        ptr = next

    return head_ref

# 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__":

    head = None

    # Create the doubly linked list
    # 18 <-> 15 <-> 8 <-> 9 <-> 14
    head = push(head, 14)
    head = push(head, 9)
    head = push(head, 8)
    head = push(head, 15)
    head = push(head, 18)

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

    head = deleteEvenDigitSumNodes(head)

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

# This code is contributed by rutvik_56

C#

// C# implementation to
// remove all the Even
// Digit Sum Nodes from a
// doubly linked list
using System;
class GFG{

// Node of the doubly
// linked list
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 the node
  Node new_node = new Node();

  // Insert 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
  // off the new node
  new_node.next = head_ref;

  // Change the 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 find the digit sum
// for a number
static int digitSum(int num)
{
  int sum = 0;
  while (num > 0)
  {
    sum += (num % 10);
    num /= 10;
  }
  return sum;
}

// 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 head_ref;

  // If the 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
  del = null;

  return head_ref;
}

// Function to to remove all
// the Even Digit Sum Nodes from a
// doubly linked list
static Node deleteEvenDigitSumNodes(Node head_ref)
{
  Node ptr = head_ref;
  Node next;

  // Iterating through the linked list
  while (ptr != null)
  {
    next = ptr.next;

    // If node's data's digit sum
    // is even
    if (!(digitSum(ptr.data) % 2 == 1))
      head_ref = 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)
{
  Node head = null;

  // Create the doubly linked list
  // 18 <. 15 <. 8 <. 9 <. 14
  head = push(head, 14);
  head = push(head, 9);
  head = push(head, 8);
  head = push(head, 15);
  head = push(head, 18);

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

// This code is contributed by shikhasingrajput

Javascript

<script>
// Javascript implementation to remove all
// the Even Digit Sum Nodes from a
// doubly linked list

// Node of the doubly linked list
class Node {

    constructor()
    {
        this.data = 0;
        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 the node
    var new_node
        = new Node();

    // Insert 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 off the new node
    new_node.next = (head_ref);

    // Change the 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 find the digit sum
// for a number
function digitSum(num)
{
    var sum = 0;
    while (num) {
        sum += (num % 10);
        num = parseInt(num/10);
    }

    return sum;
}

// 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;

    // If the 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;
}

// Function to to remove all
// the Even Digit Sum Nodes from a
// doubly linked list
function deleteEvenDigitSumNodes(head_ref)
{
    var ptr = head_ref;
    var next;

    // Iterating through the linked list
    while (ptr != null) {
        next = ptr.next;

        // If node's data's digit sum
        // is even
        if (!(digitSum(ptr.data) & 1))
            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
var head = null;

// Create the doubly linked list
// 18 <. 15 <. 8 <. 9 <. 14
head = push(head, 14);
head = push(head, 9);
head = push(head, 8);
head = push(head, 15);
head = push(head, 18);
document.write( "Original List: ");
printList(head);
head = deleteEvenDigitSumNodes(head);
document.write( "<br>Modified List: ");
printList(head);

// This code is contributed by noob2000.
</script>

Output:

Original List: 18 15 8 9 14 
Modified List: 18 9 14

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