Day 3

Mix.install([
  {:kino, "~> 0.5.0"}
])

input = Kino.Input.textarea("Paste input here:")

Part 1

priority = Enum.concat(?a..?z, ?A..?Z) |> Enum.with_index(1) |> Map.new()

input
|> Kino.Input.read()
|> String.split("\n", trim: true)
|> Enum.map(fn rucksack ->
  middle = floor(String.length(rucksack) / 2)

  {left, right} =
    rucksack
    |> String.to_charlist()
    |> Enum.split(middle)

  MapSet.intersection(MapSet.new(left), MapSet.new(right)) |> MapSet.to_list()
end)
|> Enum.reduce(0, fn [x], acc -> priority[x] + acc end)

Part 2

priority = Enum.concat(?a..?z, ?A..?Z) |> Enum.with_index(1) |> Map.new()

input
|> Kino.Input.read()
|> String.split("\n", trim: true)
|> Enum.chunk_every(3)
|> Enum.map(fn [rucksack_1, rucksack_2, rucksack_3] ->
  rucksack_1 = rucksack_1 |> String.to_charlist() |> MapSet.new()
  rucksack_2 = rucksack_2 |> String.to_charlist() |> MapSet.new()
  rucksack_3 = rucksack_3 |> String.to_charlist() |> MapSet.new()

  MapSet.intersection(rucksack_1, rucksack_2)
  |> MapSet.intersection(rucksack_3)
  |> MapSet.to_list()
end)
|> Enum.reduce(0, fn [x], acc -> priority[x] + acc end)