Untitled notebook

Mix.install([
  {:kino, "~> 0.14.2"}
])

Section

instructions = Kino.Input.textarea("instructions")

Part 1

pattern = ~r/mul\((?\d+),(?\d+)\)/

instructions
|> Kino.Input.read()
|> then(&Regex.scan(pattern, &1, capture: :all))
|> Enum.map(fn [_full_pattern, l, r] ->
  String.to_integer(l) * String.to_integer(r)
end)
|> Enum.sum()

Part 2

defmodule Part2 do
  @moduledoc "I wanted to use python for today but part 2 was much better suited to Elixir"

  @pattern ~r/\Amul\((?\d+),(?\d+)\)/

  def running(""), do: 0

  def running("don't()" <> rest) do
    not_running(rest)
  end

  def running("mul(" <> rest = text) do
    with %{"l" => l, "r" => r} <- Regex.named_captures(@pattern, text),
         {left, ""} <- Integer.parse(l),
         {right, ""} <- Integer.parse(r) do
      left * right + running(rest)
    else
      _ -> running(rest)
    end
  end

  def running(<<_::utf8>> <> rest), do: running(rest)

  def mul_first_digit("," <> rest, digits), do: {parse_digits(digits), rest}

  def mul_first_digit(<> <> rest, digits) do
    mul_first_digit(rest, [<> | digits])
  end

  def mul_second_digit(")" <> rest, digits), do: {parse_digits(digits), rest}

  def mul_second_digit(<> <> rest, digits) do
    mul_first_digit(rest, [<> | digits])
  end

  def not_running(""), do: 0
  def not_running("do()" <> rest), do: running(rest)
  def not_running(<<_::utf8>> <> rest), do: not_running(rest)

  def parse_digits(iolist) do
    iolist
    |> Enum.reverse()
    |> IO.iodata_to_binary()
    |> String.to_integer()
  end
end

instructions
|> Kino.Input.read()
|> Part2.running()