using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var addressList = new AddressRepository().GetAddresses();

        var uniqueCities = getUniqueCities(addressList);

    }

    private static HashSet<Address> getUniqueCities(List<Address> addresses)

    {

        throw new NotImplementedException("Implement me please");

    }

}

​

​

​

public class Address 

{

    public string Country { get; set;}

    public string City { get; set;} 

    public string Region { get; set;} 

    public string StreetAddress { get; set;} 

}

​

​

public class AddressRepository 

{

    public List<Address> GetAddresses()

    {

        return new List<Address> {

            new Address { Country = "USA", Region = "California", City = "LA", StreetAddress = "Boston st. 23" },

            new Address { Country = "Ukraine", Region = "Zaporizka", City = "Zaporizhia", StreetAddress = "Ladozka 23" },

            new Address { Country = "Poland", Region = "Lower Silesia", City = "Wroclaw", StreetAddress = "Legnicka 25" },

        };

    }

}