day03

Part 1

defmodule Rucksack do
  def compartments(line) do
    mid_pos = div(String.length(line), 2)

    line
    |> String.to_charlist()
    |> Enum.split(mid_pos)
  end

  def item_priority(char) when char >= ?a and char <= ?z, do: char - ?a + 1
  def item_priority(char) when char >= ?A and char <= ?Z, do: 26 + char - ?A + 1
end

File.stream!("./2022/day03input.txt")
|> Stream.map(&String.trim/1)
|> Stream.map(&Rucksack.compartments/1)
|> Stream.flat_map(fn {a, b} ->
  diff = List.myers_difference(a, b)
  Enum.uniq(diff[:eq])
end)
|> Stream.map(&Rucksack.item_priority/1)
|> Enum.sum()

Part 2

defmodule Rucksack do
  def item_priority(char) when char >= ?a and char <= ?z, do: char - ?a + 1
  def item_priority(char) when char >= ?A and char <= ?Z, do: 26 + (char - ?A) + 1
end

File.stream!("./2022/day03input.txt")
|> Stream.map(&String.trim/1)
|> Stream.map(&String.to_charlist/1)
|> Stream.chunk_every(3)
|> Stream.flat_map(fn [a, b, c] ->
  a = MapSet.new(a)
  b = MapSet.new(b)
  c = MapSet.new(c)

  a
  |> MapSet.intersection(b)
  |> MapSet.intersection(c)
  |> Enum.to_list()
end)
|> Stream.map(&Rucksack.item_priority/1)
|> Enum.sum()