sign_distribution

clng.exs

defmodule Challenge do
  def sign_distribution(numbers) do
    numbers
      |> Enum.reduce({%{neg: 0, pos: 0, zero: 0}, 0}, &update_frequencies/2)
      |> calculate_percentage
  end

  defp update_frequencies(number, {frequencies, total}) do
    {Map.update!(frequencies, sign(number), &(&1 + 1)), total + 1}
  end

  defp sign(n) when n > 0, do: :pos
  defp sign(n) when n < 0, do: :neg
  defp sign(_),            do: :zero

  defp calculate_percentage({%{neg: neg, pos: pos, zero: zero}, total}) do
    %{neg:  pcnt(neg, total),
      pos:  pcnt(pos, total),
      zero: pcnt(zero, total)}
  end

  defp pcnt(n, total), do: 1.0 * (total / n)
end

[1,2,3,0,0,0,-1,-10]
  |> Challenge.sign_distribution
  |> IO.inspect

explicit_recursion.exs

defmodule Challenge2 do
  @spec sign_distribution([Integer.t]) :: Map.t
  def sign_distribution(numbers), do: do_sign_distribution(numbers, 0, 0, 0, 0)

  defp do_sign_distribution([], total, pos, neg, zero) do
    %{pos:  pcnt(pos, total),
      neg:  pcnt(neg, total),
      zero: pcnt(zero, total)}
  end

  defp do_sign_distribution([n | ns], total, pos, neg, zero) do
    new_total = total + 1

    cond do
      n > 0 -> do_sign_distribution(ns, new_total, pos + 1, neg, zero)
      n < 0 -> do_sign_distribution(ns, new_total, pos, neg + 1, zero)
      true  -> do_sign_distribution(ns, new_total, pos, neg, zero + 1)
    end
  end

  defp pcnt(n, total), do: 1.0 * (total / n)
end