BinaryGap in Elixir

binary_gap.ex

defmodule BinaryGap do
  def max(number) when is_number(number) do
    number
    |> Integer.to_string(2)
    |> calculate()
  end

  defp calculate(binary, count \\ -1, max \\ 0)
  defp calculate("1" <> remaining, count, max) do
    calculate(remaining, 0, Enum.max([max, count]))
  end
  defp calculate("0" <> remaining, count, max) when count >= 0 do
    calculate(remaining, count + 1, max)
  end
  defp calculate("0" <> remaining, count, max) when count < 0 do
    calculate(remaining, count, max)
  end
  defp calculate("", _count, max) do
    max
  end
end