AoC20/lib/day6/day6.ex

defmodule Day6 do
  @example """
  abc

  a
  b
  c

  ab
  ac

  a
  a
  a
  a

  b
  """

  def part1(example \\ false) do
    get_answer(example, &MapSet.union/2)
  end

  def part2(example \\ false) do
    get_answer(example, &MapSet.intersection/2)
  end

  def get_answer(example, combiner) do
    if(example, do: @example, else: File.read!("lib/day6/input.txt"))
    |> String.trim()
    |> String.split("\n\n")
    |> Enum.map(fn group -> answers_to_count(group, combiner) end)
    |> Enum.map(&MapSet.size/1)
    |> Enum.sum()
  end

  def answers_to_count(group, combiner) do
    people =
      group
      |> String.split("\n")
      |> Enum.map(fn person ->
        person
        |> String.to_charlist()
        |> MapSet.new()
      end)

    people
    |> Enum.drop(1)
    |> Enum.reduce(List.first(people), combiner)
  end
end