ZCW-PhoneBook/PhoneBook.java

import java.util.*;

/**
 * Created by leon on 1/23/18.
 */
public class PhoneBook {
  String name;
  String phoneNumber;
  TreeMap<String, ArrayList<String>> phoneBook = new TreeMap<>();

  public PhoneBook(TreeMap<String, ArrayList<String>> phoneBook) {
    this.phoneBook = phoneBook;
  }

  public PhoneBook(){}

  public void add(String name, String phoneNumber){
    ArrayList<String> list;

    if (!phoneBook.containsKey(name)) {
      list = new ArrayList<>();
      phoneBook.put(name, list);
    }
    else
    {
      list = phoneBook.get(name);
      list.add(phoneNumber);
      phoneBook.replace(name, list);
    }
  }

  public void remove(String name){
    phoneBook.remove(name);
  }

  public String lookup(String name){
    ArrayList<String> numbers = phoneBook.get(name);
    StringBuilder sb = new StringBuilder();

    for (int i=0; i<numbers.size(); i++) {
      sb.append(numbers.get(i));
      if (i == numbers.size()-1) {
        break;
      } else {
        sb.append(", ");
      }
    }
    sb.append("");
    return sb.toString();
  }

  public String reverseLookup(String phoneNumber) {
    for (Map.Entry<String, ArrayList<String>> e : phoneBook.entrySet()) {
      String name = e.getKey();
      ArrayList<String> numbers = e.getValue();

      for (String s : numbers) {
        if (s == phoneNumber) {
          return name;
        }
      }
    }
    return "Name not found";
  }

  public String display() {
    StringBuilder sb = new StringBuilder();

    for (Map.Entry<String, ArrayList<String>> e : phoneBook.entrySet()){
      String name = e.getKey();
      ArrayList<String> numbers = e.getValue();

      sb.append(name).append(" ");

      for (int i=0; i<numbers.size(); i++) {
        sb.append(numbers.get(i));
        if (i == numbers.size()-1) {
          break;
        } else {
          sb.append(", ");
        }
      }
      sb.append("");
    }
    return sb.toString();
  }
}