doublelinkedlist.cpp

#include <iostream>

class Node {
public:
    int data;
    Node* next;
    Node* prev;
    Node(int value) {
        data = value;
        next = nullptr;
        prev = nullptr;
    }
};

class DoublyLinkedList {
private:
    Node* head;
    Node* tail;
public:
    DoublyLinkedList() {
        head = nullptr;
        tail = nullptr;
    }

    bool isEmpty() {
        return head == nullptr;
    }

    void insertAtHead(int value) {
        Node* newNode = new Node(value);
        if (isEmpty()) {
            head = newNode;
            tail = newNode;
        } else {
            newNode->next = head;
            head->prev = newNode;
            head = newNode;
        }
    }

    void insertAtTail(int value) {
        Node* newNode = new Node(value);
        if (isEmpty()) {
            head = newNode;
            tail = newNode;
        } else {
            tail->next = newNode;
            newNode->prev = tail;
            tail = newNode;
        }
    }

    void deleteAtHead() {
        if (isEmpty()) {
            std::cout << "List is empty" << std::endl;
            return;
        }

        Node* temp = head;
        head = head->next;
        if (head != nullptr) {
            head->prev = nullptr;
        } else {
            tail = nullptr;
        }
        delete temp;
    }

    void deleteAtTail() {
        if (isEmpty()) {
            std::cout << "List is empty" << std::endl;
            return;
        }

        Node* temp = tail;
        tail = tail->prev;
        if (tail != nullptr) {
            tail->next = nullptr;
        } else {
            head = nullptr;
        }
        delete temp;
    }

    void printForward() {
        Node* temp = head;
        while (temp != nullptr) {
            std::cout << temp->data << " ";
            temp = temp->next;
        }
        std::cout << std::endl;
    }

    void printBackward() {
        Node* temp = tail;
        while (temp != nullptr) {
            std::cout << temp->data << " ";
            temp = temp->prev;
        }
        std::cout << std::endl;
    }
};

int main() {
    DoublyLinkedList list;
    list.insertAtHead(3);
    list.insertAtHead(2);
    list.insertAtHead(1);
    list.insertAtTail(4);
    list.insertAtTail(5);
    list.printForward(); // output: 1 2 3 4 5
    list.printBackward(); // output: 5 4 3 2 1
    list.deleteAtHead();
    list.deleteAtTail();
    list.printForward(); // output: 2 3 4
    list.printBackward(); // output: 4 3 2
    return 0;
}
//java
public class DoublyLinkedList {
    private Node head;
    private Node tail;

    private class Node {
        private int data;
        private Node prev;
        private Node next;

        public Node(int data) {
            this.data = data;
            this.prev = null;
            this.next = null;
        }
    }

    public DoublyLinkedList() {
        this.head = null;
        this.tail = null;
    }

    public boolean isEmpty() {
        return head == null;
    }

    public void addFirst(int data) {
        Node newNode = new Node(data);

        if (isEmpty()) {
            tail = newNode;
        } else {
            head.prev = newNode;
        }

        newNode.next = head;
        head = newNode;
    }

    public void addLast(int data) {
        Node newNode = new Node(data);

        if (isEmpty()) {
            head = newNode;
        } else {
            tail.next = newNode;
            newNode.prev = tail;
        }

        tail = newNode;
    }

    public void deleteFirst() {
        if (isEmpty()) {
            throw new NoSuchElementException();
        }

        if (head == tail) {
            head = null;
            tail = null;
        } else {
            head = head.next;
            head.prev = null;
        }
    }

    public void deleteLast() {
        if (isEmpty()) {
            throw new NoSuchElementException();
        }

        if (head == tail) {
            head = null;
            tail = null;
        } else {
            tail = tail.prev;
            tail.next = null;
        }
    }

    public void printList() {
        if (isEmpty()) {
            System.out.println("The list is empty.");
            return;
        }

        Node current = head;
        while (current != null) {
            System.out.print(current.data + " ");
            current = current.next;
        }
        System.out.println();
    }
}