day03.livemd

Rucksack Reorganization

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

Input

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

Part 1

input = Kino.Input.read(input)

rucksacks =
  input
  |> String.trim()
  |> String.split("\n")
  |> Enum.map(fn s ->
    len = String.length(s)
    n = div(len, 2)
    {String.slice(s, 0, n), String.slice(s, n, n)}
  end)

priority = fn
  [ch] when ch >= ?a and ch <= ?z -> 1 + ch - ?a
  [ch] when ch >= ?A and ch <= ?Z -> ch - ?A + 1 + 26
end

Enum.map(rucksacks, fn {a, b} ->
  a = MapSet.new(String.to_charlist(a))
  b = MapSet.new(String.to_charlist(b))
  MapSet.intersection(a, b) |> MapSet.to_list()
end)
|> Enum.map(priority)
|> Enum.sum()

Part 2

rucksacks =
  input
  |> String.trim()
  |> String.split("\n")
  |> Enum.chunk_every(3)

rucksacks
|> Enum.map(fn [a, b, c] ->
  a = MapSet.new(String.to_charlist(a))
  b = MapSet.new(String.to_charlist(b))
  c = MapSet.new(String.to_charlist(c))

  a
  |> MapSet.intersection(b)
  |> MapSet.intersection(c)
  |> MapSet.to_list()
end)
|> Enum.map(priority)
|> Enum.sum()