2023 - day 4

Mix.install([
  {:kino, "~> 0.11.3"}
])

Section

sample_input = """
Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11
"""

puzzle_input = Kino.Input.textarea("input")

puzzle_input = Kino.Input.read(puzzle_input)

Part 1

defmodule Day4.Part1 do
  def solve(input_str) do
    input_str
    |> parse()
    |> Enum.map(&scoring/1)
    |> Enum.sum()
  end

  def parse(input_str) do
    input_str
    |> String.split("\n", trim: true)
    |> Enum.map(&parse_line/1)
  end

  defp scoring(%{winning: winning, holding: holding}) do
    win = MapSet.new(winning)
    hol = MapSet.new(holding)

    win
    |> MapSet.intersection(hol)
    |> MapSet.size()
    |> then(&if(&1 > 0, do: :math.pow(2, &1 - 1) |> round(), else: 0))
  end

  defp parse_line(line) do
    ["Card " <> card_index_str, winning_num_str, holding_str] = String.split(line, [": ", " | "])
    card_index = to_int(card_index_str)
    winning = winning_num_str |> String.split(" ", trim: true) |> Enum.map(&amp;to_int/1)
    holding = holding_str |> String.split(" ", trim: true) |> Enum.map(&amp;to_int/1)
    %{id: card_index, winning: winning, holding: holding}
  end

  defp to_int(str), do: str |> String.trim() |> Integer.parse() |> elem(0)
end

Day4.Part1.solve(puzzle_input)

Part 2

defmodule Day4.Part2 do
  def solve(input_str) do
    input_str
    |> parse()
    |> process()
    |> Map.values()
    |> Enum.sum()
  end

  defp process(card_list) do
    card_list
    |> Enum.reduce_while(%{}, fn card, instance_map ->
      copies = Map.get(instance_map, card.id, 0)

      if copies + card.matching > 0 do
        instance_map =
          for i <- 1..card.matching//1, reduce: instance_map do
            acc ->
              Map.update(acc, card.id + i, copies + 1, &amp;(&amp;1 + copies + 1))
          end
          |> Map.update(card.id, 1, &amp;(&amp;1 + 1))

        {:cont, instance_map}
      else
        {:halt, instance_map}
      end
    end)
  end

  def parse(input_str) do
    input_str
    |> String.split("\n", trim: true)
    |> Enum.map(&amp;parse_line/1)
  end

  defp parse_line(line) do
    ["Card " <> card_index_str, winning_num_str, holding_str] = String.split(line, [": ", " | "])
    card_index = to_int(card_index_str)
    winning = winning_num_str |> String.split(" ", trim: true) |> Enum.map(&amp;to_int/1)
    holding = holding_str |> String.split(" ", trim: true) |> Enum.map(&amp;to_int/1)
    %{id: card_index, winning: winning, holding: holding, matching: matching(winning, holding)}
  end

  defp matching(winning, holding) do
    win = MapSet.new(winning)
    hol = MapSet.new(holding)

    win
    |> MapSet.intersection(hol)
    |> MapSet.size()
  end

  defp to_int(str), do: str |> String.trim() |> Integer.parse() |> elem(0)
end

Day4.Part2.solve(puzzle_input)