Day 4

Mix.install([
  {:kino_aoc, "~> 0.1.5"}
])

Input

{:ok, puzzle_input} =
  KinoAOC.download_puzzle("2023", "4", System.fetch_env!("LB_AOC_SESSION"))

scratchcards =
  puzzle_input
  |> String.split("\n")
  |> Enum.map(fn s ->
    Regex.scan(~r/\d+(?![:\d])/, s)
    |> Enum.flat_map(& &1)
    |> Enum.map(&String.to_integer/1)
    |> Enum.split(10)
    |> Tuple.to_list()
    |> Enum.map(&MapSet.new/1)
  end)

Part 1

win_counts =
  scratchcards
  |> Enum.map(&apply(MapSet, :intersection, &1))
  |> Enum.map(&Enum.count/1)

win_counts
|> Enum.filter(&(&1 > 0))
|> Enum.map(&(:math.pow(2, &1 - 1) |> trunc))
|> Enum.sum()

Part 2

win_counts
|> Enum.reverse()
|> Enum.reduce([], fn wins, acc ->
  [1 + Enum.sum(Enum.take(acc, wins)) | acc]
end)
|> Enum.sum()