Day 07: – AoC 22

input = File.stream!("/Users/pw/src/weiland/adventofcode/2022/input/07.txt")
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" |> String.split("\n")

Part One

stream = fn input ->
  input
  |> Stream.map(&String.trim/1)
  |> Stream.map(&String.split(&1, " "))
  |> Stream.map(fn [indicator | rest] ->
    cond do
      "$" == indicator && ["cd", ".."] == rest -> {:up, nil}
      "$" == indicator && ["cd"] == Enum.take(rest, 1) -> {:goto, List.first(Enum.drop(rest, 1))}
      "$" == indicator && ["ls"] == rest -> {:ls, nil}
      "dir" == indicator -> {:directory, List.first(rest)}
      # drop file-name
      true -> {:file, String.to_integer(indicator)}
    end
  end)
end

build_tree = fn stream ->
  stream
  |> Enum.map_reduce([], fn t, acc ->
    {a, v} = t

    cond do
      a == :up -> {Tuple.append(t, []), Enum.drop(acc, 1)}
      a == :goto -> {Tuple.append(t, []), [v | acc]}
      true -> {Tuple.append(t, acc), acc}
    end
  end)
  |> then(fn {lst, _rst} -> lst end)
  |> Enum.reject(fn {a, _, _} -> a == :up || a == :goto || a == :ls || a == :directory end)
  |> Enum.reduce(%{}, fn {_action, size, path}, acc ->
    0..(Enum.count(path) - 1)
    |> Enum.map(fn pos -> Enum.drop(path, pos) end)
    |> Enum.reduce(acc, fn dir, ac ->
      Map.merge(ac, Map.new([{dir, size}]), fn _k, a, b -> a + b end)
    end)
  end)
  |> Enum.map(fn {_path, size} -> size end)
end

limit = 100_000

part_one = fn stream ->
  build_tree.(stream)
  |> Enum.reject(&(&1 > limit))
  |> Enum.sum()
end

IO.inspect(part_one.(stream.(test_input)) == 95437, label: "smoke test")

part_one.(stream.(input))

Part Two

system_max = 70_000_000
min_needed = 30_000_000

part_two = fn stream ->
  tree = build_tree.(stream)
  limit = min_needed - system_max + Enum.max(tree)

  tree
  |> Enum.reject(&amp;(&amp;1 < limit))
  |> Enum.min()
end

IO.inspect(part_two.(stream.(test_input)) == 24_933_642, label: "smoke test")

part_two.(stream.(input))