ZCW-PhoneBook/PhoneBook.java

 
import java.util.*;
/**
 * Created by leon on 1/23/18.
 */
public class PhoneBook {
    private Map<String, ArrayList<String>> phoneBook;
    
    public PhoneBook() {
        phoneBook = new TreeMap<String, ArrayList<String>>();
    }
    
    public ArrayList<String> add(String name, String number) {
        if (phoneBook.get(name) == null) {
            phoneBook.put(name, new ArrayList<String>());
        }
        phoneBook.get(name).add(number);
        
        return phoneBook.get(name);
    }
    
    public ArrayList<String> lookup(String name) {
        return phoneBook.get(name);
    }
    
    public String reverseLookup(String phoneNumber) {
        String name = "not found";
        for (Map.Entry<String, ArrayList<String>> entry : phoneBook.entrySet()) {
            for (String numbers : entry.getValue()) {
                if (numbers.equals(phoneNumber)) name = entry.getKey();
            }
        }
        return name;
    }
    
    public String display() {
        StringBuilder phoneNumbers = new StringBuilder();
        for (Map.Entry<String, ArrayList<String>> entry : phoneBook.entrySet()) {
            phoneNumbers.append(entry.getKey() + " ");
            for (String number : entry.getValue()) {
                phoneNumbers.append(number + " ");
            }
            phoneNumbers.append("\n");
        }
        return phoneNumbers.toString();
    }
    
}