import java.util.*;

public class PhoneBook
{
    public static int hashFunction(String name){
        int hash = 0;
        for(int i=0; i<name.length(); i++){
            hash = hash*10 + name.charAt(i);
        }
        hash = hash % 499;
        return hash;
    }

    public static void main(String args[]){
        Hashtable<Integer, String> phonebook = new Hashtable<>();
        List<String> names = new ArrayList<String>();
        Scanner sc = new Scanner(System.in);

        int choice = -1;
        String number;
        String name;

        while(choice != 0){
            System.out.println("What do you want to do?");
            System.out.println("1. Add a contact");
            System.out.println("2. Show a contact");
            System.out.println("3. Delete a contact");
            System.out.println("4. Show all contacts");
            System.out.println("5. Exit");
            choice = sc.nextInt();

            switch(choice){
                case 1:
                    System.out.println("Add Phone Number:");
                    number = sc.next();
                    System.out.println("Name:");
                    name = sc.next();
                    names.add(name);
                    phonebook.put(hashFunction(name), number);
                    System.out.println("Added successfully.");
                    break;
                case 2:
                    System.out.println("Name:");
                    name = sc.next();
                    number = phonebook.get(hashFunction(name));
                    System.out.println("Phone Number: " +  number);
                    break;
                case 3:
                    System.out.println("Name:");
                    name = sc.next();
                    names.remove(name);
                    phonebook.remove(hashFunction(name));
                    System.out.println("Removed successfully.");
                    break;
                case 4:
                    if(phonebook.size() > 0){
                        System.out.println(phonebook.size() + " contacts saved");
                        for(String i : names){
                            System.out.println(i + ": " + phonebook.get(hashFunction(i)));
                        }
                    }
                    else
                        System.out.println("You haven't added any contacts yet.");
            }
        }
    }
}