using System;

using System.Collections.Generic;

​

public class Names

{

    public static string[] FindCommon(string[] names1, string[] names2)

    {

        HashSet<string> hSet1 = new HashSet<string>(names1);

        HashSet<string> hSet2 = new HashSet<string>(names2);

        hSet1.UnionWith(hSet2);

        String[] stringArray = new String[hSet1.Count];

        hSet1.CopyTo(stringArray);

        return stringArray;

    }

    public static void Main(string[] args)

    {

        string[] names1 = new string[] {"Ava", "Emma", "Olivia"};

        string[] names2 = new string[] {"Olivia", "Sophia", "Emma"};

        Console.WriteLine(string.Join(", ", Names.FindCommon(names1, names2))); // should print Ava, Emma, Olivia, Sophia

    }

}