Day 7

Mix.install([:kino])

Input

input = Kino.Input.textarea("")

Pre-work

defmodule FileSystem do
  def new(commands) do
    Enum.reduce(commands, {%{[] => 0}, []}, fn
      ["$", "cd", ".."], {fs, [_ | path]} -> {fs, path}
      ["$", "cd", "/"], {fs, _} -> {fs, []}
      ["$", "cd", dir], {fs, path} -> {fs, [dir | path]}
      ["$", "ls"], {fs, path} -> {fs, path}
      ["dir", dir], {fs, path} -> {Map.put_new(fs, [dir | path], 0), path}
      [size, _], {fs, path} -> {add(fs, path, String.to_integer(size)), path}
    end)
  end

  def add(fs, [], size), do: Map.update!(fs, [], &(&1 + size))
  def add(fs, path, size), do: fs |> Map.update!(path, &(&1 + size)) |> add(tl(path), size)
end

{fs, _} =
  input
  |> Kino.Input.read()
  |> String.split("\n")
  |> Enum.map(&String.split/1)
  |> FileSystem.new()

dir_sizes = Map.values(fs)

Part 1

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

Part 2

space_to_free = 30_000_000 - 70_000_000 + fs[[]]
dir_sizes |> Enum.filter(&(&1 >= space_to_free)) |> Enum.min()