# Replace even nodes of a doubly linked list with the elements of array

• Difficulty Level : Basic
• Last Updated : 30 Aug, 2022

Given a doubly linked list and an array with only odd values. Both are of equal size N. The task is replace all node which have even value with the Array elements from left to right.

Examples:

Input : List = 6 9 8 7 4
Arr[] = {3, 5, 23, 17, 1}
Output : List = 3 9 5 7 23
Input : List = 9 14 7 12 8 13
Arr[] = {5, 1, 17, 21, 11, 7}
Output : List = 9 5 7 1 17 13

Approach: The idea is to traverse the nodes of the doubly linked list one by one and get the pointer of the nodes having even data then replace by the value of the array and increment the index of the array and move to the next node in the linked list.
Below is the implementation of above approach:

## C++

 `// C++ implementation to create``// odd doubly linked list``#include ``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 = (Node*)``malloc``(``sizeof``(``struct` `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 off 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 make all node is odd``void` `makeOddNode(Node** head_ref, ``int` `A[], ``int` `n)``{``    ``Node* ptr = *head_ref;``    ``Node* next;``    ``int` `i = 0;``    ``// traverse list till last node``    ``while` `(ptr != NULL) {``        ``next = ptr->next;``        ``// check if node is even then``        ``// replace it and increment in i``        ``if` `(ptr->data % 2 == 0) {``            ``ptr->data = A[i];``            ``i++;``        ``}``        ``ptr = next;``    ``}``    ``// return sum of nodes which is divided by K``}``// 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 to test above``int` `main()``{``    ``// start with the empty list``    ``Node* head = NULL;` `    ``// create the doubly linked list``    ``// 6 <=> 9 <=> 8 <=> 7 <=> 4``    ``int` `Arr[] = { 3, 5, 23, 17, 1 };``    ``push(&head, 4);``    ``push(&head, 7);``    ``push(&head, 8);``    ``push(&head, 9);``    ``push(&head, 6);``    ``int` `n = ``sizeof``(Arr) / ``sizeof``(Arr[0]);``    ``cout << ``"Original List: "``;``    ``printList(head);``    ``cout << endl;``    ``makeOddNode(&head, Arr, n);``    ``cout << ``"New odd List: "``;``    ``printList(head);``}`

## Java

 `// Java implementation to create``// odd 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 off 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 make all node is odd``static` `Node makeOddNode(Node head_ref, ``int` `A[], ``int` `n)``{``    ``Node ptr = head_ref;``    ``Node next;``    ``int` `i = ``0``;``    ``// traverse list till last node``    ``while` `(ptr != ``null``)``    ``{``        ``next = ptr.next;``        ` `        ``// check if node is even then``        ``// replace it and increment in i``        ``if` `(ptr.data % ``2` `== ``0``)``        ``{` `            ``ptr.data = A[i];``            ``i++;``        ``}``        ``ptr = next;``    ``}``    ` `    ``// return sum of nodes which is divided by K``    ``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``    ``// 6 <=> 9 <=> 8 <=> 7 <=> 4``    ``int` `Arr[] = { ``3``, ``5``, ``23``, ``17``, ``1` `};``    ``head = push(head, ``4``);``    ``head = push(head, ``7``);``    ``head = push(head, ``8``);``    ``head = push(head, ``9``);``    ``head = push(head, ``6``);``    ``int` `n = Arr.length;``    ``System.out.print( ``"Original List: "``);``    ``printList(head);``    ``System.out.println();``    ``head = makeOddNode(head, Arr, n);``    ``System.out.print(``"New odd List: "``);``    ``printList(head);``}``}` `// This code is contributed by Arnab Kundu`

## Python3

 `# Python3 implementation to``# create odd doubly linked list` `# Node of the doubly linked list``class` `Node:``    ` `    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data``        ``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 node``    ``new_node ``=` `Node(new_data)` `    ``# link the old list off 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 make all node is odd``def` `makeOddNode(head_ref, A, n):` `    ``ptr ``=` `head_ref``    ``i ``=` `0``    ` `    ``# traverse list till last node``    ``while` `ptr !``=` `None``:``        ` `        ``next` `=` `ptr.``next``        ` `        ``# check if node is even then``        ``# replace it and increment in i``        ``if` `ptr.data ``%` `2` `=``=` `0``:``            ``ptr.data ``=` `A[i]``            ``i ``+``=` `1``        ` `        ``ptr ``=` `next``    ` `    ``# return sum of nodes which is divided by K` `# 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``    ``# 6 <=> 9 <=> 8 <=> 7 <=> 4``    ``Arr ``=` `[``3``, ``5``, ``23``, ``17``, ``1``]``    ``head ``=` `push(head, ``4``)``    ``head ``=` `push(head, ``7``)``    ``head ``=` `push(head, ``8``)``    ``head ``=` `push(head, ``9``)``    ``head ``=` `push(head, ``6``)``    ``n ``=` `len``(Arr)``    ` `    ``print``(``"Original List:"``, end ``=` `" "``)``    ``printList(head)``    ``print``()``    ` `    ``makeOddNode(head, Arr, n)``    ``print``(``"New odd List:"``, end ``=` `" "``)``    ``printList(head)` `# This code is contributed by Rituraj Jain`

## C#

 `// C# implementation to create``// odd 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 off 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 make all node is odd``static` `Node makeOddNode(Node head_ref, ``int` `[]A, ``int` `n)``{``    ``Node ptr = head_ref;``    ``Node next;``    ``int` `i = 0;``    ` `    ``// traverse list till last node``    ``while` `(ptr != ``null``)``    ``{``        ``next = ptr.next;``        ` `        ``// check if node is even then``        ``// replace it and increment in i``        ``if` `(ptr.data % 2 == 0)``        ``{` `            ``ptr.data = A[i];``            ``i++;``        ``}``        ``ptr = next;``    ``}``    ` `    ``// return sum of nodes which is divided by K``    ``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``    ``// 6 <=> 9 <=> 8 <=> 7 <=> 4``    ``int` `[]Arr = { 3, 5, 23, 17, 1 };``    ``head = push(head, 4);``    ``head = push(head, 7);``    ``head = push(head, 8);``    ``head = push(head, 9);``    ``head = push(head, 6);``    ``int` `n = Arr.Length;``    ``Console.WriteLine( ``"Original List: "``);``    ``printList(head);``    ``Console.WriteLine();``    ``head = makeOddNode(head, Arr, n);``    ``Console.WriteLine(``"New odd List: "``);``    ``printList(head);``}``}` `// This code contributed by Rajput-Ji`

## Javascript

 ``

Output:

```Original List: 6 9 8 7 4
New odd List: 3 9 5 7 23```

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

Auxiliary Space: O(1) because it is using constant space

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