Delete All Even Nodes from a Doubly Linked List in C++

In this tutorial, we are going to learn how to delete all prime nodes from a doubly linked list.

Let's see the steps to solve the problem.

• Write struct with data, prev and next pointers.

• Write a function to insert the node into the doubly linked list.

• Initialize the doubly linked list with dummy data.

• Iterate over the doubly linked list. Find whether the current node data is even or not.

• If the current data is even, then delete the node.

• Write a function to delete the node. Consider the following three cases while deleting the node.

  • If the node is head node, then move the head to next node.

  • If the node is middle node, then link the next node to the previous node

  • If the node is end node, then remove the previous node link.

Example

Let's see the code.

 Live Demo

#include <bits/stdc++.h>
using namespace std;
struct Node {
   int data;
   Node *prev, *next;
};
void insertNode(Node** head_ref, int new_data) {
   Node* new_node = (Node*)malloc(sizeof(struct Node));
   new_node->data = new_data;
   new_node->prev = NULL;
   new_node->next = (*head_ref);
   if ((*head_ref) != NULL) {
      (*head_ref)->prev = new_node;
   }
   (*head_ref) = new_node;
}
void deleteNode(Node** head_ref, Node* del) {
   if (*head_ref == NULL || del == NULL) {
      return;
   }
   if (*head_ref == del) {
      *head_ref = del->next;
   }
   if (del->next != NULL) {
      del->next->prev = del->prev;
   }
   if (del->prev != NULL) {
      del->prev->next = del->next;
   }
   free(del);
   return;
}
void deleteEvenNodes(Node** head_ref) {
   Node* temp = *head_ref;
   Node* next;
   while (temp != NULL) {
      next = temp->next;
      if (temp->data % 2 == 0) {
         deleteNode(head_ref, temp);
      }
      temp = next;
   }
}
void printLinkedList(Node* head) {
   while (head != NULL) {
      cout << head->data << " -> ";
      head = head->next;
   }
}
int main() {
   Node* head = NULL;
   insertNode(&head, 1);
   insertNode(&head, 2);
   insertNode(&head, 3);
   insertNode(&head, 4);
   insertNode(&head, 5);
   insertNode(&head, 6);
   cout << "Linked List before deletion:" << endl;
   printLinkedList(head);
   deleteEvenNodes(&head);
   cout << "\nLinked List after deletion:" << endl;
   printLinkedList(head);
}

Output

If you execute the above program, then you will get the following result.

Linked List before deletion:
6 -> 5 -> 4 -> 3 -> 2 -> 1 ->
Linked List after deletion:
5 -> 3 -> 1 ->

Conclusion

If you have any queries in the tutorial, mention them in the comment section.