roman-numbers

elixir/roman-numerals/lib/roman_numerals.ex

@@ -0,0 +1,33 @@
+defmodule RomanNumerals do
+  @doc """
+  Convert the number to a roman number.
+  """
+  @romans %{
+    1 => ["I", "X", "C", "M"],
+    2 => ["II", "XX", "CC", "MM"],
+    3 => ["III",  "XXX", "CCC", "MMM"],
+    4 => ["IV",  "XL", "CD"],
+    5 => ["V",  "L", "D"],
+    6 => ["VI",  "LX", "DC"],
+    7 => ["VII",  "LXX", "DCC"],
+    8 => ["VIII",  "LXXX", "DCCC"],
+    9 => ["IX",  "XC", "CM"]
+  }
+
+  @spec numeral(pos_integer) :: String.t()
+  def numeral(number) do
+    number
+    |> Integer.digits()
+    |> Enum.reverse()
+    |> Enum.with_index(&to_roman_digit/2)
+    |> Enum.reverse()
+    |> Enum.join()
+  end
+
+  defp to_roman_digit(0, _index), do: ""
+  defp to_roman_digit(digit, index) do
+    @romans
+    |> Map.fetch!(digit)
+    |> Enum.at(index)
+  end
+end