— Day 3: Mull It Over —

Mix.install([{:kino_aoc, "~> 0.1"}])

Setup

{:ok, puzzle_input} =
  KinoAOC.download_puzzle("2024", "3", System.fetch_env!("LB_AOC_SESSION_COOKIE"))

defmodule MullItOver do
  def mul_pattern(), do: ~r/mul\(\d+,\d+\)/
  def mul_do_dont_pattern(), do: ~r/mul\(\d+,\d+\)|do\(\)|don't\(\)/

  def parse(input, pattern) do
    pattern
    |> Regex.scan(input)
    |> List.flatten()
  end

  def parse_product(command) do
    ~r/\d+/
    |> Regex.scan(command)
    |> List.flatten()
    |> Enum.map(&String.to_integer/1)
    |> Enum.product()
  end

  def maybe_mull("don't()", {_, acc}), do: {:dont, acc}
  def maybe_mull("do()", {_, acc}), do: {:do, acc}
  def maybe_mull("mul" <> nums, {:do, acc}), do: {:do, parse_product(nums) + acc}
  def maybe_mull("mul" <> _nums, {:dont, acc}), do: {:dont, acc}
end

Part 1

import MullItOver

puzzle_input
|> parse(mul_pattern())
|> Enum.map(&parse_product/1)
|> Enum.sum()

Part 2

import MullItOver

puzzle_input
|> parse(mul_do_dont_pattern())
|> Enum.reduce({:do, 0}, &maybe_mull/2)
|> elem(1)