Day 03

Section

defmodule Day03 do
  @priorities [?a..?z, ?A..?Z] |> Enum.concat() |> Enum.with_index(1) |> Map.new()

  def part1(input_path) do
    input_path
    |> File.stream!()
    |> Stream.map(&String.trim/1)
    |> Stream.map(&:binary.bin_to_list/1)
    |> Stream.map(&Enum.split(&1, div(length(&1), 2)))
    |> Stream.map(fn {f, r} ->
      Enum.uniq(f -- f -- r)
    end)
    |> Stream.flat_map(fn intersection ->
      Enum.map(intersection, &@priorities[&1])
    end)
    |> Enum.sum()
  end

  def part2(input_path) do
    input_path
    |> File.stream!()
    |> Stream.map(&String.trim/1)
    |> Stream.map(&:binary.bin_to_list/1)
    |> Stream.map(&MapSet.new/1)
    |> Stream.chunk_every(3)
    |> Stream.flat_map(fn group ->
      Enum.reduce(group, &MapSet.intersection/2)
    end)
    |> Stream.map(&@priorities[&1])
    |> Enum.sum()
  end
end

input_path = "#{__DIR__}/day03.txt"

Day03.part1(input_path)

Day03.part2(input_path)