[Sync Iteration] elixir/roman-numerals/2

solutions/elixir/roman-numerals/2/lib/roman_numerals.ex

@@ -0,0 +1,39 @@
+defmodule RomanNumerals do
+  @doc """
+  Convert the number to a roman number.
+  """
+  @spec numeral(pos_integer) :: String.t()
+  def numeral(number), do: reduce_to_roman(number)
+
+  defp reduce_to_roman(number, numeral \\ "")
+  defp reduce_to_roman(0, numeral), do: numeral
+  defp reduce_to_roman(number, numeral) when number >= 1000,
+    do: reduce_to_roman(number - 1000, numeral <> "M")
+
+  defp reduce_to_roman(number, numeral) when number >= 500 and number < 900,
+    do: reduce_to_roman(number - 500, numeral <> "D")
+
+  defp reduce_to_roman(number, numeral) when number >= 900 or number >= 400,
+    do: reduce_to_roman(number + 100, numeral <> "C")
+
+  defp reduce_to_roman(number, numeral) when number >= 100,
+    do: reduce_to_roman(number - 100, numeral <> "C")
+
+  defp reduce_to_roman(number, numeral) when number >= 50 and number < 90,
+    do: reduce_to_roman(number - 50, numeral <> "L")
+
+  defp reduce_to_roman(number, numeral) when number >= 90 or number >= 40,
+    do: reduce_to_roman(number + 10, numeral <> "X")
+
+  defp reduce_to_roman(number, numeral) when number >= 10,
+    do: reduce_to_roman(number - 10, numeral <> "X")
+
+  defp reduce_to_roman(number, numeral) when number >= 5 and number < 9,
+    do: reduce_to_roman(number - 5, numeral <> "V")
+
+  defp reduce_to_roman(number, numeral) when number == 9 or number == 4,
+    do: reduce_to_roman(number + 1, numeral <> "I")
+
+  defp reduce_to_roman(number, numeral) when number > 0,
+    do: reduce_to_roman(number - 1, numeral <> "I")
+end