Advent of Code 2024 - Day 23

Mix.install([{:kino, github: "livebook-dev/kino"}])

kino_input = Kino.Input.textarea("Please paste your input file: ")

Part 1

input = Kino.Input.read(kino_input)

input
|> String.split("\n", trim: true)
|> Enum.reduce(%{}, fn connection, connections ->
  [computer1, computer2] = String.split(connection, "-")

  connections
  |> Map.update(computer1, [computer2], fn conns -> [computer2 | conns] end)
  |> Map.update(computer2, [computer1], fn conns -> [computer1 | conns] end)
end)
|> then(fn network_map ->
  network_map
  |> Map.keys()
  |> Enum.flat_map(fn computer1 ->
    connections = Map.get(network_map, computer1, [])

    for computer2 <- connections,
        computer3 <- connections,
        computer2 != computer3,
        computer3 in Map.get(network_map, computer2, []),
        do: Enum.sort([computer1, computer2, computer3])
  end)
  |> Enum.uniq()
  |> Enum.filter(fn [a, b, c] ->
    Enum.any?([a, b, c], fn name -> String.starts_with?(name, "t") end)
  end)
  |> Enum.count()
end)

Part 2

input = Kino.Input.read(kino_input)

input
|> String.split("\n", trim: true)
|> Enum.reduce(%{}, fn connection, connections ->
  [computer1, computer2] = String.split(connection, "-")

  connections
  |> Map.update(computer1, MapSet.new([computer2]), &MapSet.put(&1, computer2))
  |> Map.update(computer2, MapSet.new([computer1]), &MapSet.put(&1, computer1))
end)
|> then(fn network_map ->
  network_map
  |> Enum.map(fn {computer1, connections1} ->
    connections1
    |> Enum.map(fn computer2 ->
      network_map
      |> Map.get(computer2)
      |> MapSet.intersection(connections1)
    end)
    |> Enum.concat()
    |> Enum.frequencies()
    |> Enum.sort_by(&elem(&1, 1), :desc)
    |> Enum.reduce(MapSet.new([computer1]), fn {computer, _}, group ->
      if MapSet.subset?(group, Map.get(network_map, computer)) do
        MapSet.put(group, computer)
      else
        group
      end
    end)
  end)
end)
|> Enum.max_by(&MapSet.size/1)
|> Enum.sort()
|> Enum.join(",")