Advent of Code 2022

Mix.install([
  {:req, "~> 0.3.2"}
])

Day 10

input =
  "https://adventofcode.com/2022/day/10/input"
  |> Req.get!(headers: [cookie: "session=#{System.get_env("AOC_COOKIE")}"])
  |> Map.get(:body)
  |> String.split("\n", trim: true)

sample =
  """
  addx 15
  addx -11
  addx 6
  addx -3
  addx 5
  addx -1
  addx -8
  addx 13
  addx 4
  noop
  addx -1
  addx 5
  addx -1
  addx 5
  addx -1
  addx 5
  addx -1
  addx 5
  addx -1
  addx -35
  addx 1
  addx 24
  addx -19
  addx 1
  addx 16
  addx -11
  noop
  noop
  addx 21
  addx -15
  noop
  noop
  addx -3
  addx 9
  addx 1
  addx -3
  addx 8
  addx 1
  addx 5
  noop
  noop
  noop
  noop
  noop
  addx -36
  noop
  addx 1
  addx 7
  noop
  noop
  noop
  addx 2
  addx 6
  noop
  noop
  noop
  noop
  noop
  addx 1
  noop
  noop
  addx 7
  addx 1
  noop
  addx -13
  addx 13
  addx 7
  noop
  addx 1
  addx -33
  noop
  noop
  noop
  addx 2
  noop
  noop
  noop
  addx 8
  noop
  addx -1
  addx 2
  addx 1
  noop
  addx 17
  addx -9
  addx 1
  addx 1
  addx -3
  addx 11
  noop
  noop
  addx 1
  noop
  addx 1
  noop
  noop
  addx -13
  addx -19
  addx 1
  addx 3
  addx 26
  addx -30
  addx 12
  addx -1
  addx 3
  addx 1
  noop
  noop
  noop
  addx -9
  addx 18
  addx 1
  addx 2
  noop
  noop
  addx 9
  noop
  noop
  noop
  addx -1
  addx 2
  addx -37
  addx 1
  addx 3
  noop
  addx 15
  addx -21
  addx 22
  addx -6
  addx 1
  noop
  addx 2
  addx 1
  noop
  addx -10
  noop
  noop
  addx 20
  addx 1
  addx 2
  addx 2
  addx -6
  addx -11
  noop
  noop
  noop
  """
  |> String.split("\n", trim: true)

Part 1

input
|> Enum.reduce({1, 1, []}, fn op, {cycle, x, signal_strength} ->
  case op do
    "noop" ->
      ss =
        if rem(cycle + 1 + 20, 40) == 0 do
          [(cycle + 1) * x | signal_strength]
        else
          signal_strength
        end

      {cycle + 1, x, ss}

    "addx " <> n ->
      ss =
        cond do
          rem(cycle + 1 + 20, 40) == 0 ->
            [(cycle + 1) * x | signal_strength]

          rem(cycle + 2 + 20, 40) == 0 ->
            [(cycle + 2) * (x + String.to_integer(n)) | signal_strength]

          true ->
            signal_strength
        end

      {cycle + 2, x + String.to_integer(n), ss}
  end
end)
|> elem(2)
|> Enum.sum()

Part 2

input
|> Enum.flat_map(fn
  "noop" ->
    [:noop]

  "addx " <> n ->
    [:begin_add_x, {:add_x, String.to_integer(n)}]
end)
|> Enum.reduce({1, 1}, fn op, {cycle, x} ->
  col = rem(cycle - 1, 40)
  IO.write(if col in (x - 1)..(x + 1), do: "#", else: ".")

  if rem(cycle, 40) == 0 do
    IO.puts("")
  end

  x =
    case op do
      {:add_x, n} -> x + n
      _ -> x
    end

  {cycle + 1, x}
end)

Alternate Solutions

Cleaner part 1.

input
|> Enum.flat_map(fn
  "noop" ->
    [:noop]

  "addx " <> n ->
    [:begin_add_x, {:add_x, String.to_integer(n)}]
end)
|> Enum.reduce({1, 1, []}, fn op, {cycle, x, ss} ->
  ss = if rem(cycle + 20, 40) == 0, do: [cycle * x | ss], else: ss

  x =
    case op do
      {:add_x, n} -> x + n
      _ -> x
    end

  {cycle + 1, x, ss}
end)
|> elem(2)
|> Enum.sum()