raindrops

elixir/raindrops/lib/raindrops.ex

@@ -0,0 +1,30 @@
+defmodule Raindrops do
+  @doc """
+  Returns a string based on raindrop factors.
+
+  - If the number contains 3 as a prime factor, output 'Pling'.
+  - If the number contains 5 as a prime factor, output 'Plang'.
+  - If the number contains 7 as a prime factor, output 'Plong'.
+  - If the number does not contain 3, 5, or 7 as a prime factor,
+    just pass the number's digits straight through.
+  """
+  @results [
+    {3, "Pling"},
+    {5, "Plang"},
+    {7, "Plong"}
+  ]
+
+  @spec convert(pos_integer) :: String.t()
+  def convert(number) do
+    @results
+    |> Enum.map_join(&mapper(number, &1))
+    |> case do
+      "" -> Integer.to_string(number)
+      result -> result
+    end
+  end
+
+  defp mapper(number, {factor, value}) do
+    if rem(number, factor) == 0, do: value, else: ""
+  end
+end