🎄 Year 2023 🔔 Day 04

Setup

filename = "#{__DIR__}/../../../inputs/2023/day04.txt"

parsed_lines =
  File.read!(filename)
  |> String.split("\n", trim: true)
  |> Enum.map(fn line ->
    [_, line] = String.split(line, ":")
    [w_numbers, own_numbers] = String.split(line, "|")
    w_numbers = String.split(w_numbers, " ", trim: true) |> Enum.map(&String.to_integer/1)
    own_numbers = String.split(own_numbers, " ", trim: true) |> Enum.map(&String.to_integer/1)
    {w_numbers, own_numbers}
  end)

Part 1

parsed_lines
|> Enum.map(fn {w_numbers, own_numbers} ->
  count = Enum.count(w_numbers, fn wn -> Enum.any?(own_numbers, fn on -> wn == on end) end)
  if count == 0, do: 0, else: Integer.pow(2, count - 1)
end)
|> Enum.sum()

Section

defmodule Helper do
  def process_scratch_cards(cards, used_cards \\ [])

  def process_scratch_cards([], used_cards),
    do: used_cards |> Enum.map(&elem(&1, 2)) |> Enum.sum()

  def process_scratch_cards([{_, _, 0} | _], used_cards),
    do: used_cards |> Enum.map(&elem(&1, 2)) |> Enum.sum()

  def process_scratch_cards([card = {w_numbers, own_numbers, count} | cards], used_cards) do
    add_to = Enum.count(w_numbers, fn wn -> Enum.any?(own_numbers, fn on -> wn == on end) end)

    new_cards =
      cards
      |> Enum.with_index(fn e = {w_numbers, own_numbers, current_count}, i ->
        if i < add_to, do: {w_numbers, own_numbers, current_count + count}, else: e
      end)

    process_scratch_cards(new_cards, [card | used_cards])
  end
end

parsed_lines
|> Enum.map(fn {w_numbers, own_numbers} ->
  {w_numbers, own_numbers, 1}
end)
|> Helper.process_scratch_cards()