Program.cs

static void Main(string[] args)
{
    var factory = new MailPieceFactory();
    var zipCodes = new List<int>();

    for (int index = 0; index < 23458333; index++)
    {
        zipCodes.Add(index % 100000);
        var randomPiece = factory.GetPiece(GetRandomKey());
        string pieceStatistics = randomPiece.GetStatistics(zipCodes[index]);
        Console.Write(pieceStatistics);
    }

    Console.ReadLine();
}

private static char GetRandomKey()
{
    return new Random().Next() % 2 == 0 ? 'P' : 'L';
}