🎄 Year 2022 🔔 Day 10

Problem

Parse input

filename = "#{__DIR__}/../../../inputs/2022/day10.txt"

instructions =
  File.stream!(filename)
  |> Enum.map(&String.trim/1)
  |> Enum.flat_map(fn instruction ->
    case String.split(instruction) do
      ["noop"] -> [:noop]
      ["addx", count] -> [:addx, {:addx, String.to_integer(count)}]
    end
  end)

parsed_steps =
  instructions
  |> Enum.map(fn instruction ->
    case instruction do
      :noop -> 0
      :addx -> 0
      {:addx, count} -> count
    end
  end)

Shared code

Part One

parsed_steps
|> Enum.scan(1, &(&1 + &2))
|> Enum.zip(instructions)
|> then(&[{0, "asdf"} | &1])
|> Enum.with_index(fn {a, b}, i -> {a, b, i} end)
|> Enum.take_every(20)
|> Enum.drop_every(2)
|> Enum.map(fn state ->
  case state do
    {register, {:addx, count}, i} -> {register - count, i}
    {register, _, i} -> {register, i}
  end
end)
|> Enum.map(fn {register, index} -> register * index end)
|> Enum.sum()

Part two

rem(46, 40)

parsed_steps
|> Enum.scan(1, &(&1 + &2))
|> Enum.zip(instructions)
|> Enum.with_index(fn {a, b}, i -> {a, b, i} end)
|> Enum.map(fn state = {_, _, index} ->
  register =
    case state do
      {register, {:addx, count}, i} -> register - count
      {register, _, i} -> register
    end

  index = rem(index, 40)

  if register >= index - 1 && register <= index + 1, do: "#", else: "."
end)
|> Enum.chunk_every(40)
|> Enum.map(&Enum.join/1)
|> Enum.join("\n")
|> IO.puts()