collatz_conjecture.exs

defmodule Collatz do
  def conjecture(int) when int < 2 do
    raise ArgumentError, message: "Requires an integer value greater than 1"
  end

  def conjecture(int), do: conjecture(int, 0)

  defp conjecture(1, 1), do: "Reduced to 1 in 1 step"

  defp conjecture(1, steps), do: "Reduced to 1 in #{steps} steps"

  defp conjecture(int, steps) when rem(int, 2) == 0 do
    conjecture(div(int, 2), steps + 1)
  end

  defp conjecture(int, steps) do
    conjecture(3 * int + 1, steps + 1)
  end
end