LinkedList.java

package project;

class Node {
    int data;
    Node next;

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

public class LinkedList {
    private Node head;

    // Insert at the beginning
    void insertAtBeginning(int data) {
        Node newNode = new Node(data);
        newNode.next = head;
        head = newNode;
    }

    // Insert at the end
    void insertAtEnd(int data) {
        Node newNode = new Node(data);
        if (head == null) {
            head = newNode;
            return;
        }
        Node temp = head;
        while (temp.next != null) {
            temp = temp.next;
        }
        temp.next = newNode;
    }

    // Insert after a specific key
    void insertAfter(int key, int data) {
        Node temp = head;
        while (temp != null && temp.data != key) {
            temp = temp.next;
        }
        if (temp != null) {
            Node newNode = new Node(data);
            newNode.next = temp.next;
            temp.next = newNode;
        } else {
            System.out.println("Key " + key + " not found.");
        }
    }

    // Delete at the beginning
    void deleteAtBeginning() {
        if (head != null) {
            head = head.next;
        }
    }

    // Delete at the end
    void deleteAtEnd() {
        if (head == null) return;
        if (head.next == null) {
            head = null;
            return;
        }
        Node temp = head;
        while (temp.next.next != null) {
            temp = temp.next;
        }
        temp.next = null;
    }

    // Delete by key
    void deleteByKey(int key) {
        if (head == null) return;
        if (head.data == key) {
            head = head.next;
            return;
        }
        Node temp = head;
        while (temp.next != null && temp.next.data != key) {
            temp = temp.next;
        }
        if (temp.next != null) {
            temp.next = temp.next.next;
        } else {
            System.out.println("Key " + key + " not found.");
        }
    }

    // Display the list
    void display() {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " -> ");
            temp = temp.next;
        }
        System.out.println("null");
        System.out.println();
    }
}