Day4

Part 1

defmodule Day4 do
  def parse_cards(cards) do
    cards
    |> String.split("|")
    |> Enum.map(&Enum.map(String.split(&1, " ", trim: true), fn x -> String.to_integer(x) end))
  end

  def winning_numbers(card) do
    [winning, normal] = card

    n =
      normal
      |> Enum.map(fn card ->
        Enum.any?(winning, fn win -> win == card end)
      end)
      |> Enum.count(fn x -> x end)

    n
  end

  def winning_rec(cards, values) do
    values
    |> Enum.with_index()
    |> Enum.map(fn {val, idx} ->
      1 + calculate_rec(cards, idx, val)
    end)
  end

  def calculate_rec(calculated_cards, from, value) do
    case value do
      0 ->
        0

      _ ->
        1..value
        |> Enum.map(fn x ->
          1 + calculate_rec(calculated_cards, from + x, Enum.at(calculated_cards, from + x))
        end)
        |> Enum.sum()
    end
  end
end

{:module, Day4, <<70, 79, 82, 49, 0, 0, 15, ...>>, {:calculate_rec, 3}}

file = File.read!("../input/day4.txt")

file
|> String.split("\n", trim: true)
|> Enum.map(&Regex.replace(~r/Card +[0-9]+:/, &1, ""))
|> Enum.map(&Day4.parse_cards/1)
|> Enum.map(&Day4.winning_numbers/1)
|> Enum.map(&Bitwise.<<<(1, &1 - 1))
|> Enum.sum()

25010

Part 2

file = File.read!("../input/day4.txt")

calculated_cards =
  file
  |> String.split("\n", trim: true)
  |> Enum.map(&Regex.replace(~r/Card +[0-9]+:/, &1, ""))
  |> Enum.map(&Day4.parse_cards/1)
  |> Enum.map(&Day4.winning_numbers/1)

Day4.winning_rec(calculated_cards, calculated_cards)
|> Enum.sum()

9924412