# 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

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++ 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 = (Node*)` `malloc` `(` `sizeof` `(` `struct` `Node)); ` ` ` ` ` `// put in the data ` ` ` `new_node->data = new_data; ` ` ` ` ` `// since we are adding at the begining, ` ` ` `// 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 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); ` `} ` |

*chevron_right*

*filter_none*

**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.

## Recommended Posts:

- Delete all the nodes from a doubly linked list that are smaller than a given value
- Delete all nodes from the doubly linked list which are divisible by K
- Delete all Prime Nodes from a Doubly Linked List
- Delete all the nodes from the doubly linked list that are greater than a given value
- Delete all occurrences of a given key in a doubly linked list
- Delete a node in a Doubly Linked List
- Delete a Doubly Linked List node at a given position
- Delete N nodes after M nodes of a linked list
- Rotate Doubly linked list by N nodes
- Product of all prime nodes in a Doubly Linked List
- Sum of all nodes in a doubly linked list divisible by a given number K
- Delete all the even nodes of a Circular Linked List
- Delete alternate nodes of a Linked List
- Product of all nodes in a doubly linked list divisible by a given number K
- Replace even nodes of a doubly linked list with the elements of array

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