roman numerals elixir

elixir/roman-numerals/lib/roman_numerals.ex

@@ -0,0 +1,39 @@
+defmodule RomanNumerals do
+  @values %{
+    "I" => 1,
+    "IV" => 4,
+    "V" => 5,
+    "IX" => 9,
+    "X" => 10,
+    "XL" => 40,
+    "L" => 50,
+    "XC" => 90,
+    "C" => 100,
+    "CD" => 400,
+    "D" => 500,
+    "CM" => 900,
+    "M" => 1000
+  }
+
+  @doc """
+  Convert the number to a roman number.
+  """
+  @spec numeral(pos_integer) :: String.t()
+  def numeral(number) do
+    number
+    |> Stream.unfold(fn
+      0 -> nil
+      n -> get_max(n)
+    end)
+    |> Enum.join()
+  end
+
+  defp get_max(n) do
+    numeral =
+      Map.keys(@values)
+      |> Enum.filter(&(Map.get(@values, &1) <= n))
+      |> Enum.max_by(&Map.get(@values, &1))
+
+    {numeral, n - Map.get(@values, numeral)}
+  end
+end