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Section

input =
  File.read!("./input.txt")
  |> String.split("$ ")
  |> Enum.drop(1)
  |> Enum.map(&String.trim/1)

files =
  input
  |> Enum.map(&String.split(&1, "\n"))
  |> Enum.map(fn l -> Enum.map(l, &String.split(&1)) end)
  |> Enum.reduce({"/", []}, fn
    [["cd", dir] | _], {cwd, acc} ->
      {Path.expand(Path.join(cwd, dir)), acc}

    [["ls"] | files], {cwd, acc} ->
      {
        cwd,
        files
        |> Enum.filter(fn [d, _] -> d != "dir" end)
        |> Enum.map(fn [size, name] -> {Path.join(cwd, name), String.to_integer(size)} end)
        |> Enum.concat(acc)
      }
  end)
  |> then(fn {_, files} -> files end)

defmodule X do
  def to_the_root(dirs, "/", _), do: dirs

  def to_the_root(dirs, dir, size) do
    dir = Path.dirname(dir)

    Map.update(dirs, dir, size, &(&1 + size))
    |> X.to_the_root(dir, size)
  end
end

dirs = Enum.reduce(files, %{}, fn {dir, size}, dirs -> X.to_the_root(dirs, dir, size) end)

Map.values(dirs)
|> Enum.filter(&amp;(&amp;1 <= 100_000))
|> Enum.sum()

total = 70_000_000
wanted = 30_000_000
available = total - dirs["/"]

Map.values(dirs)
|> Enum.filter(&(&1 >= wanted - available))
|> Enum.min()