pyramid_calculator.ex

defmodule PyramidCalculator do

  @doc """
  iex> PyramidCalculator.pyramid_prices_percents([1, 2, 3], 10)
  [10.0, 33.33333333333333, 56.666666666666664]
  iex> PyramidCalculator.pyramid_prices_percents([1, 2, 3], 40)
  [40.0, 33.333333333333336, 26.666666666666668]
  iex> PyramidCalculator.pyramid_prices_percents([1, 3, 7, 22], 5)
  [5.0, 10.517241379310345, 21.551724137931036, 62.93103448275862]
  """
  def pyramid_prices_percents(prices, initial_percent) do

      total_pyramid_percent = 100 - Enum.count(prices) * initial_percent
      total_distance = total_distance(prices)

      calc = fn (price) ->
        initial_percent + (price / total_distance) * total_pyramid_percent
      end

      abs_prices(prices) |> Enum.map(calc)
  end

  defp total_distance(prices), do: prices |> abs_prices |> Enum.sum
  defp abs_prices([h|_] = xs), do: xs |> Enum.map(&(abs(&1 - h)))
end