Day 7

Mix.install([
  {:req, "~> 0.3.2"},
  {:vega_lite, "~> 0.1.6"},
  {:kino_vega_lite, "~> 0.1.6"}
])

alias VegaLite, as: Vl

day = 7

aoc_session = System.fetch_env!("LB_AOC_SESSION")
input_url = "https://adventofcode.com/2022/day/#{day}/input"
{:ok, %{body: input}} = Req.get(input_url, headers: [cookie: "session=#{aoc_session}"])

Input

test_input = """
$ cd /
$ ls
dir a
14848514 b.txt
8504156 c.dat
dir d
$ cd a
$ ls
dir e
29116 f
2557 g
62596 h.lst
$ cd e
$ ls
584 i
$ cd ..
$ cd ..
$ cd d
$ ls
4060174 j
8033020 d.log
5626152 d.ext
7214296 k
"""

Part 1

defmodule Part1 do
  def parse_line("$ cd /"), do: :root
  def parse_line("$ cd .."), do: :pop_dir
  def parse_line("$ cd " <> dir), do: {:push_dir, dir}
  def parse_line("$ ls"), do: :ls
  def parse_line("dir " <> dir), do: {:ls_output_dir, dir}

  def parse_line(line) do
    [size_str, filename] = String.split(line, " ")
    {:ls_output_file, %{filename: filename, size: String.to_integer(size_str)}}
  end

  def inc_for_dirs(sizemap, dirs, size) do
    dirs
    |> Enum.reduce(sizemap, fn dir, acc ->
      Map.update(acc, dir, size, &amp;(&amp;1 + size))
    end)
  end
end

# input = test_input

{_dirs, sizemap} =
  input
  |> String.split("\n", trim: true)
  |> Enum.reduce({["/"], %{}}, fn line, {dirs, sizemap} ->
    [cwd | _] = dirs

    case Part1.parse_line(line) do
      {:push_dir, dirname} -> {["#{cwd}#{dirname}/" | dirs], sizemap}
      :pop_dir -> {Enum.drop(dirs, 1), sizemap}
      {:ls_output_file, %{size: size}} -> {dirs, Part1.inc_for_dirs(sizemap, dirs, size)}
      _ -> {dirs, sizemap}
    end
  end)

sizemap
|> Map.reject(fn {_dir, size} -> size > 100_000 end)
|> Map.values()
|> Enum.sum()

Part 2

total_disk_space = 70_000_000
unused_space = total_disk_space - sizemap["/"]
space_still_needed = 30_000_000 - unused_space

sizemap
|> Map.filter(fn {_dir, size} -> size > space_still_needed end)
|> Map.values()
|> Enum.min()