Day 3

Mix.install([
  {:kino_aoc, git: "https://github.com/ljgago/kino_aoc"}
])

Helper

{:ok, puzzle_input} = KinoAOC.download_puzzle("2022", "3", System.fetch_env!("LB_AOC_SESSION"))

puzzle_input =
  puzzle_input
  |> String.split("\n", trim: true)

Part 1

duplicate_finder = fn {first_string, second_string} ->
  first_string = String.split(first_string, "", trim: true)
  second_string = String.split(second_string, "", trim: true)

  MapSet.intersection(MapSet.new(first_string), MapSet.new(second_string))
  |> MapSet.to_list()
  |> List.to_string()
end

duplicates =
  puzzle_input
  |> Enum.map(fn rucksack_items ->
    String.split_at(rucksack_items, div(String.length(rucksack_items), 2))
  end)
  |> Enum.map(fn items -> duplicate_finder.(items) end)

defmodule Priority do
  @characters_list ((?a..?z |> Enum.map(& &1)) ++ (?A..?Z |> Enum.map(& &1)))
                   |> List.to_string()
                   |> String.split("", trim: true)

  def get_priority(character) do
    Enum.find_index(@characters_list, fn c -> c == character end) + 1
  end
end

Enum.reduce(duplicates, 0, fn char, sum ->
  sum + Priority.get_priority(char)
end)

Part 2

puzzle_input =
  puzzle_input
  |> Enum.chunk_every(3)
  |> Enum.reduce(0, fn [first, second, third], sum ->
    first_string = String.split(first, "", trim: true)
    second_string = String.split(second, "", trim: true)
    third_string = String.split(third, "", trim: true)

    duplicate =
      MapSet.intersection(MapSet.new(first_string), MapSet.new(second_string))
      |> MapSet.intersection(MapSet.new(third_string))
      |> MapSet.to_list()
      |> List.to_string()

    sum + Priority.get_priority(duplicate)
  end)