Advent of Code 2022 - Day 10

Day 10: Cathode-Ray Tube

Description

Utils

defmodule Load do
  def file(path) do
    File.read!(__DIR__ <> path)
    |> String.split("\n", trim: true)
  end

  def string(value) do
    value |> String.split("\n", trim: true)
  end
end

Input

input = Load.file("/data/day10.txt")

Part 1

Find the signal strength during the 20th, 60th, 100th, 140th, 180th, and 220th cycles. What is the sum of these six signal strengths?

defmodule Part1 do
  def run([], signal) do
    signal
  end

  def run([instruction | input], [x | _] = signal) do
    instruction = instruction |> String.split(" ", trim: true)

    case instruction do
      [_command | [value]] ->
        value = value |> String.to_integer()
        signal = [x + value, x] ++ signal
        run(input, signal)

      _ ->
        run(input, [x | signal])
    end
  end

  def signal_strength(signal) do
    Enum.at(signal, 19) * 20 +
      Enum.at(signal, 59) * 60 +
      Enum.at(signal, 99) * 100 +
      Enum.at(signal, 139) * 140 +
      Enum.at(signal, 179) * 180 +
      Enum.at(signal, 219) * 220
  end
end

input
|> Part1.run([1])
|> Enum.reverse()
|> Part1.signal_strength()

Result

14520

Part 2

Render the image given by your program. What eight capital letters appear on your CRT?

defmodule Part2 do
  def render([], pixels) do
    pixels
  end

  def render([x | signal], pixels) do
    pixel_x = pixels |> Enum.count() |> rem(40)

    if pixel_x <= x + 1 and pixel_x >= x - 1 do
      render(signal, ["#" | pixels])
    else
      render(signal, ["." | pixels])
    end
  end
end

input
|> Part1.run([1])
|> Enum.reverse()
|> Part2.render([])
|> Enum.reverse()
|> Enum.chunk_every(40)
|> Enum.map(&amp;Enum.join/1)
|> Enum.each(&amp;IO.puts/1)

Result

###..####.###...##..####.####...##.###..
#..#....#.#..#.#..#....#.#.......#.#..#.
#..#...#..###..#......#..###.....#.###..
###...#...#..#.#.##..#...#.......#.#..#.
#....#....#..#.#..#.#....#....#..#.#..#.
#....####.###...###.####.####..##..###..