import java.util.HashSet;
import java.util.Iterator;
import java.util.Scanner;

public class StudentManager {

    public static void main(String[] args) {

        HashSet<String> students = new HashSet<>();
        Scanner sc = new Scanner(System.in);

        int choice;

        do {
            System.out.println("\n===== Student Management System =====");
            System.out.println("1. Add student name");
            System.out.println("2. Display all student names");
            System.out.println("3. Remove a student name");
            System.out.println("4. Exit");
            System.out.print("Enter your choice: ");

            choice = sc.nextInt();
            sc.nextLine(); // consume newline

            switch (choice) {

                case 1:
                    System.out.print("Enter student name to add: ");
                    String name = sc.nextLine();

                    if (students.add(name)) {
                        System.out.println("Student added successfully.");
                    } else {
                        System.out.println("Duplicate entry! Student already exists.");
                    }
                    break;

                case 2:
                    System.out.println("\n--- Student List ---");

                    if (students.isEmpty()) {
                        System.out.println("No students in the list.");
                    } else {
                        Iterator<String> it = students.iterator();
                        while (it.hasNext()) {
                            System.out.println(it.next());
                        }
                    }
                    break;

                case 3:
                    System.out.print("Enter student name to remove: ");
                    String removeName = sc.nextLine();

                    if (students.remove(removeName)) {
                        System.out.println("Student removed successfully.");
                    } else {
                        System.out.println("Student not found.");
                    }
                    break;

                case 4:
                    System.out.println("Exiting application. Goodbye!");
                    break;

                default:
                    System.out.println("Invalid choice! Please try again.");
            }

        } while (choice != 4);

        sc.close();
    }
}