ZCW-PhoneBook/PhoneBook.java

 
import java.util.TreeMap;
/**
 * Created by leon on 1/23/18.
 */
public class PhoneBook {
    private TreeMap<String, String> phoneBook;
    private TreeMap<String, String> reversePhoneBook;
    
    public PhoneBook() {
        phoneBook = new TreeMap<String, String>();
        reversePhoneBook = new TreeMap<String, String>();
    }
    
    public void add(String name, String phoneNumber) {
        phoneBook.put(name, phoneNumber);
        reversePhoneBook.put(phoneNumber, name);
    }
    
    public void remove(String name) {
        String phoneNumber = phoneBook.get(name);
        phoneBook.remove(name);
        reversePhoneBook.remove(phoneNumber);
    }
    
    public String lookup(String name) {
        return phoneBook.get(name) != null ? 
                                   phoneBook.get(name)
                                   : 
                                   "N/A";
    }
    
    public String reverseLookup(String phoneNumber) {
        return reversePhoneBook.get(phoneNumber) != null ? 
                                                 reversePhoneBook.get(phoneNumber)
                                                 :
                                                 "N/A";
    }
    
    public TreeMap getPhoneBook() {
        return phoneBook; 
    }
    
    public TreeMap getReversePhoneBook() {
        return reversePhoneBook;
    }
}