🎄 Year 2024 🔔 Day 03

Setup

input = File.read!("#{__DIR__}/../../../inputs/2024/day03.txt")

Part 1

regex = ~r/mul\(\d{1,3},\d{1,3}\)/

input
|> then(&Regex.scan(regex, &1))
|> Enum.map(fn [line] ->
  line
  |> then(fn "mul" <> rest -> rest end)
  |> String.trim("(")
  |> String.trim(")")
  |> String.split(",")
  |> then(fn [a, b] -> String.to_integer(a) * String.to_integer(b) end)
end)
|> Enum.sum()

Part 2

regex = ~r/(do\(\)|don't\(\)|mul\(\d{1,3},\d{1,3}\))/

input
|> then(&Regex.scan(regex, &1, capture: :first))
|> Enum.reduce(
  %{should_count: true, count: 0},
  fn [e], %{should_count: should_count, count: count} ->
    cond do
      e == "do()" ->
        %{should_count: true, count: count}

      e == "don't()" ->
        %{should_count: false, count: count}

      should_count == false ->
        %{should_count: should_count, count: count}

      true ->
        e_count =
          e
          |> then(fn "mul" <> rest -> rest end)
          |> String.trim("(")
          |> String.trim(")")
          |> String.split(",")
          |> then(fn [a, b] -> String.to_integer(a) * String.to_integer(b) end)

        %{should_count: should_count, count: count + e_count}
    end
  end
)
|> Map.fetch!(:count)