Lecture 215:- Let's Code Delete for Doubly Linked List

Below is the C++ implementation of the DoublyLinkedList class with a method to delete a node with a given key (value) from the doubly linked list:

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#include <iostream> class Node { public:    int data;    Node* next;    Node* prev;    Node(int data) : data(data), next(nullptr), prev(nullptr) {} }; class DoublyLinkedList { private:    Node* head;    Node* tail; public:    DoublyLinkedList() : head(nullptr), tail(nullptr) {}    ~DoublyLinkedList() {        Node* current = head;        while (current) {            Node* temp = current;            current = current->next;            delete temp;        }    }    void insertAtHead(int data) {        Node* newNode = new Node(data);        if (!head) {            head = newNode;            tail = newNode;        } else {            newNode->next = head;            head->prev = newNode;            head = newNode;        }    }    void insertAtTail(int data) {        Node* newNode = new Node(data);        if (!tail) {            head = newNode;            tail = newNode;        } else {            newNode->prev = tail;            tail->next = newNode;            tail = newNode;        }    }    void deleteNode(int key) {        if (!head) {            std::cout << "List is empty. Nothing to delete." << std::endl;            return;        }        Node* current = head;        while (current && current->data != key) {            current = current->next;        }        if (current && current->data == key) {            if (current->prev) {                current->prev->next = current->next;            } else {                head = current->next;            }            if (current->next) {                current->next->prev = current->prev;            } else {                tail = current->prev;            }            delete current;        } else {            std::cout << "Element with key " << key << " not found in the list." << std::endl;        }    }    void displayForward() {        if (!head) {            std::cout << "List is empty." << std::endl;            return;        }        Node* current = head;        while (current) {            std::cout << current->data << " -> ";            current = current->next;        }        std::cout << "NULL" << std::endl;    }    void displayBackward() {        if (!tail) {            std::cout << "List is empty." << std::endl;            return;        }        Node* current = tail;        while (current) {            std::cout << current->data << " -> ";            current = current->prev;        }        std::cout << "NULL" << std::endl;    } }; int main() {    DoublyLinkedList list;    list.insertAtHead(1);    list.insertAtHead(2);    list.insertAtTail(3);    list.insertAtTail(4);    list.displayForward(); // Output: 2 -> 1 -> 3 -> 4 -> NULL    list.deleteNode(3);    list.deleteNode(2);    list.displayForward(); // Output: 1 -> 4 -> NULL    return 0; }

In this implementation, we've added the deleteNode method to the DoublyLinkedList class. This method allows us to search for a node with the given key (data) in the doubly linked list and delete it. If the node with the given key is not found, it displays an error message.

In the main function, we demonstrate how to use the DoublyLinkedList class by creating a doubly linked list, inserting elements at the head and tail, and deleting nodes with specific keys using the deleteNode method. The output will be 2 -> 1 -> 3 -> 4 -> NULL for the initial list and 1 -> 4 -> NULL after the deletions.