romanize.ex

units = %{
  "0" => "0",
  "1" => "I",
  "2" => "II",
  "3" => "III",
  "4" => "IV",
  "5" => "V",
  "6" => "VI",
  "7" => "VII",
  "8" => "VIII",
  "9" => "IX"
}

tens = %{
  10 => "X",
  20 => "XX",
  20 => "XXX",
  20 => "40",,
  20 => "50",
}

test_values = ["6", "7", "21"]

result_values = ["VI", "VII", "XXI"]

defmodule Xy do
  def romanize(units, x) do
    case units[x] do
      nil ->
        more_than_nine(units, x)
      x -> 
        x
    end
  end

  def more_than_nine(units, x)
    unit = rem(x, 10)
    ten = x - unit 
    ten_string = tens[ten]
    one_string = romanize(units, unit)
    ten_string <> one_string
  end
end

our_result = Enum.map(test_values, fn(x) -> Xy.romanize(num, x) end)

IO.puts test_values
IO.puts result_values
IO.puts our_result

Cleaner:

input_values = [6, 7, 21]
expected_result = ["VI", "VII", "XXI"]

dictionary = %{
  0 => "",
  1 => "I",
  2 => "II",
  3 => "III",
  4 => "IV",
  5 => "V",
  6 => "VI",
  7 => "VII",
  8 => "VIII",
  9 => "IX",
  10 => "X",
  20 => "XX",
  30 => "XXX",
  40 => "40",
  50 => "50",
}

defmodule Xy do
  def romanize(dictionary, x) do
    remainder = rem(x, 10)
    ten = x - remainder

    lookup(dictionary, ten) <> lookup(dictionary, remainder)
  end

  def lookup(dictionary, element) do
    Map.get(dictionary, element, "")
  end
end

result = Enum.map(input_values, fn(x) -> Xy.romanize(dictionary, x) end)

IO.inspect input_values
IO.inspect expected_result
IO.inspect result