Elixir

defmodule AdventOfCode.Solution.Year2024.Day05 do
  use AdventOfCode.Solution.SharedParse

  @impl true
  def parse(input) do
    [rules, pages_list] =
      String.split(input, "\n\n", limit: 2) |> Enum.map(&String.split(&1, "\n", trim: true))

    {for(rule <- rules, do: String.split(rule, "|") |> Enum.map(&String.to_integer/1))
     |> MapSet.new(),
     for(pages <- pages_list, do: String.split(pages, ",") |> Enum.map(&String.to_integer/1))}
  end

  def part1({rules, pages_list}), do: solve(rules, pages_list, false)

  def part2({rules, pages_list}), do: solve(rules, pages_list, true)

  def solve(rules, pages_list, negate) do
    for pages <- pages_list, reduce: 0 do
      total ->
        ordered = Enum.sort(pages, &([&1, &2] in rules))

        if negate != (ordered == pages),
          do: total + Enum.at(ordered, div(length(ordered), 2)),
          else: total
    end
  end
end