ZCW-PhoneBook/PhoneBook.java

import java.util.*;

/**
 * Created by leon on 1/23/18.
 */
public class PhoneBook {
    String name;
    String phoneNumber;
    
    // create treemap(hashmap), has key String, value arrayList of Strings
    TreeMap<String, ArrayList<String>> phoneBook = new TreeMap<>();
    
    // construct an instance of phoneBook
    public PhoneBook(TreeMap<String, ArrayList<String>> phoneBook) {
        this.phoneBook = phoneBook;
    }
    
    // default constructor
    public PhoneBook(){}

    public void add(String name, String phoneNumber){
        // if phonebook does NOT contain key(name), put name on list
        if (!phoneBook.containsKey(name)) {
            ArrayList<String> list = new ArrayList<>();
            list.add(phoneNumber);
            phoneBook.put(name, list);
            // or else, create tempoary arraylist and add phonenumber
        } else {
            ArrayList<String> temp = phoneBook.get(name);
            temp.add(phoneNumber);
            
            //(key,old key,new key)
            phoneBook.replace(name, phoneBook.get(name), temp);
        }   
    }

    public void remove(String name, String phoneNumber){
        
        ArrayList<String> list = phoneBook.get(name);
        // if only one number, remove name
        if(list.size() == 1) {
            phoneBook.remove(name);
            
            // or else create temp arraylist and remove phonenumber/replace
            // in list with parameters (name, list, temp)
        } else {
            ArrayList<String> temp = phoneBook.get(name);
            temp.remove(phoneNumber);
            phoneBook.replace(name,list,temp);
        }
    }

    public void removeRecord(String name) {
        phoneBook.remove(name);
    }
    
    // lookup returns list of phonenumbers for given name
    public ArrayList<String> lookup(String name){
        return phoneBook.get(name);
    }
    
    
    public String reverseLookup(String phoneNumber) {
        // for each entry in phonebook, lookup array of name/number
        for (Map.Entry<String, ArrayList<String>> entry : phoneBook.entrySet()) {
            // gets name
            String name = entry.getKey();
            // gets list of numbers
            ArrayList<String> list = entry.getValue();
            // if number equals the number we are looking for, return name
            for (String number: list) {
                if (number.equals(phoneNumber)) {
                    return name;
                } 
            }           
        }
        return "Not found";
    }

    public String display() {
        // build a string to display
        StringBuilder sb = new StringBuilder();
        
        // For (string, phone number) entry, iterate thru phoneBook.entrySet
        for (Map.Entry<String, ArrayList<String>> entry : phoneBook.entrySet()){
            
            String name = entry.getKey();
            ArrayList<String> numbers = entry.getValue();
            
            // when key got, add name to space " "
            sb.append(name).append(" ");

            // for each number in element, append to name
            for (int i = 0; i < numbers.size(); i++) {
                sb.append(numbers.get(i));

                // append a space if i is not the last number in list
                if (i != numbers.size()-1) {
                    sb.append(" ");
                }
            }
            sb.append("\n");
        }
        return sb.toString();
    }
}