AoC 2022 Day 3

Mix.install([
  {:kino, "~> 0.7.0"},
  {:kino_vega_lite, "~> 0.1.6"}
])

Section

input_field = Kino.Input.textarea("Puzzle input")

input = Kino.Input.read(input_field)

Part 1

alphabet =
  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
  |> String.graphemes()

get_priority = fn item ->
  Enum.find_index(alphabet, &match?(^item, &1)) + 1
end

require Integer

rucksacks =
  input
  |> String.split("\n")
  |> Enum.map(&String.graphemes/1)
  |> Enum.map(fn rucksack ->
    length = Enum.count(rucksack)
    # Just to be sure
    true = Integer.is_even(length)
    Enum.split(rucksack, Integer.floor_div(length, 2))
  end)

shared_items =
  rucksacks
  |> Enum.map(fn {first, second} ->
    first_set = MapSet.new(first)
    second_set = MapSet.new(second)
    [shared_item] = MapSet.intersection(first_set, second_set) |> MapSet.to_list()
    shared_item
  end)

shared_items
|> Enum.map(get_priority)
|> Enum.sum()

Part 2

groups =
  input
  |> String.split("\n")
  |> Enum.map(&String.graphemes/1)
  |> Enum.map(&MapSet.new/1)
  |> Enum.chunk_every(3)
  |> Enum.map(fn group ->
    [item] =
      group
      |> Enum.reduce(&MapSet.intersection/2)
      |> MapSet.to_list()

    item
  end)
  |> Enum.map(get_priority)
  |> Enum.sum()