ZCW-PhoneBook/PhoneBook.java

import java.util.TreeMap;
import java.util.*;
/**
 * Created by leon on 1/23/18.
 */
public class PhoneBook {
    TreeMap<String, ArrayList<String>> pb;

    public PhoneBook(){
        pb = new TreeMap<>();   

    }

    public void addElement(String name, String phoneNumber){
        ArrayList<String> aList  =  pb.containsKey(name) ? pb.get(name): new ArrayList<String>();
        aList.add(phoneNumber + "\n");
        pb.put(name, aList);
    }

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

    public String lookUp(String name){
        StringBuilder look = new StringBuilder();

        for(String element: this.pb.get(name)){
            
                look.append(element);
                
            
        }
        return look.toString();
    }

    public String reverseLookup(String phoneNumber){
        String gettingThatValue = null;
        for(Map.Entry<String,ArrayList<String>> element: pb.entrySet()){
            if(element.getValue().contains(phoneNumber)){
                gettingThatValue = element.getKey();
                break;
            }
        }

        return gettingThatValue;
    }

    public void display(){
        for(Map.Entry<String,ArrayList<String>> element:pb.entrySet()){
            System.out.print(element.getKey() + ":" + element.getValue().toString());
        }
    }

}