Day 10

Section

noop
addx 3
addx -5

yields

    1  2  3  4  5  6
[1, 1, 1, 1, 4, 4, -1]

defmodule Day10 do
  def part1(input) do
    [20, 60, 100, 140, 180, 220]
    |> Enum.map(&(&1 * input[&1]))
    |> Enum.sum()
  end

  def part2(input) do
    1..241
    |> Enum.chunk_every(40, 40, :discard)
    |> Enum.each(fn chunk ->
      chunk
      |> Enum.map(fn cycle ->
        pos = rem(cycle, 40) - 1

        if abs(pos - input[cycle]) <= 1 do
          IO.ANSI.format([:blue_background, :blue, "%"], true)
        else
          IO.ANSI.format([:red_background, :red, " "], true)
        end
      end)
      |> IO.puts()
    end)
  end

  def parse_input(path) do
    path
    |> File.stream!()
    |> Stream.map(&amp;String.trim/1)
    |> Enum.flat_map(fn
      "addx " <> s -> [0, String.to_integer(s)]
      "noop" -> [0]
    end)
    |> to_prefix_sum([1, 1])
    |> Enum.with_index()
    |> Map.new(fn {s, i} -> {i, s} end)
  end

  defp to_prefix_sum([h | t], acc), do: to_prefix_sum(t, [h + hd(acc) | acc])
  defp to_prefix_sum([], acc), do: Enum.reverse(acc)
end

input = Day10.parse_input("#{__DIR__}/day10.txt")

Day10.part1(input)

Day10.part2(input)