1.exs

defmodule World do
  defp prev_height(p1, p2) do
    cond do
      p1 == 0 -> p2
      p2 == 0 -> p1
      true -> if Dice.success?(0.7), do: p1, else: p2
    end
  end

  def inc([]) do
    [10, 10, 10, 10, 10]
  end

  def inc([p1, p2 | _] = cols) do
    prev = prev_height p1, p2

    cur = if Dice.success? 0.7 do
      prev + Dice.roll 2
    else
      if Dice.success? 0.8 do
        prev - Dice.roll 2
      else
        prev - Dice.roll prev
      end
    end

    cur = Enum.max([cur, 0])
    cur = Enum.min([cur, 20])

    [cur | cols]
  end
end