AOC 2023 - Day 4

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

Input

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

Day 4 Implementation

defmodule Day4 do
  def parse_card(card_string) do
    ["Card" <> card_id_string, card_number_string] = String.split(card_string, ": ")
    [card_numbers_string, winning_numbers_string] = String.split(card_number_string, " | ")

    card_numbers =
      card_numbers_string
      |> String.split()

    winning_numbers =
      winning_numbers_string
      |> String.split()

    matching_numbers =
      MapSet.intersection(
        MapSet.new(card_numbers),
        MapSet.new(winning_numbers)
      )

    no_of_matches = MapSet.size(matching_numbers)

    points =
      case no_of_matches do
        0 ->
          0

        1 ->
          1

        num ->
          0..(num - 2)
          |> Enum.reduce(1, fn _num, acc -> acc * 2 end)
      end

    card_id = String.trim(card_id_string) |> String.to_integer()

    won_card_ids =
      case no_of_matches do
        0 ->
          []

        1 ->
          [card_id + 1]

        _ ->
          1..no_of_matches
          |> Enum.map(fn num -> card_id + num end)
      end

    %{
      card_id: card_id,
      card_numbers: card_numbers,
      winning_numbers: winning_numbers,
      matching_numbers: matching_numbers,
      points: points,
      won_card_ids: won_card_ids
    }
  end

  def get_all_won_cards(card, all_cards) do
    won_cards = Enum.filter(all_cards, fn c -> c.card_id in card.won_card_ids end)
    [card | Enum.map(won_cards, fn c -> get_all_won_cards(c, all_cards) end)]
  end
end

cards =
  puzzle_input
  |> String.split("\n")
  |> Enum.filter(fn line -> line != "" end)
  |> Enum.map(fn line -> Day4.parse_card(line) end)

Part 1 - Solution

Enum.reduce(cards, 0, fn card, acc -> acc + card.points end)

Part 2 - Solution

cards
|> Enum.map(fn card -> Day4.get_all_won_cards(card, cards) end)
|> List.flatten()
|> length