Day 07

Part 1

File.stream!("./2022/day07input.txt")
|> Stream.map(&String.trim/1)
|> Stream.drop(1)
|> Enum.reduce({[0], 0}, fn
  "$ cd ..", {[cur_size, parent_size | rest], total_size} ->
    new_path = [cur_size + parent_size | rest]

    if cur_size <= 100_000 do
      {new_path, total_size + cur_size}
    else
      {new_path, total_size}
    end

  "$ cd " <> _dir, {path, total_size} ->
    {[0 | path], total_size}

  "$ ls", fs ->
    fs

  "dir " <> _, fs ->
    fs

  file_entry, {[cur_size | rest], total_size} ->
    [raw_size, _] = String.split(file_entry)
    {[cur_size + String.to_integer(raw_size) | rest], total_size}
end)
|> elem(1)

Part 2

input = File.stream!("./2022/day07input.txt")

file_entry_size = fn file_entry ->
  [raw_size, _] = String.split(file_entry)
  String.to_integer(raw_size)
end

total_space = 70_000_000
required_space = 30_000_000

used_space =
  input
  |> Enum.map(fn
    "$ " <> _ -> 0
    "dir " <> _ -> 0
    file_entry -> file_entry_size.(file_entry)
  end)
  |> Enum.sum()

available_space = total_space - used_space
need_to_clean = required_space - available_space

input
|> Stream.map(&amp;String.trim/1)
|> Stream.drop(1)
|> Enum.reduce({[0], total_space}, fn
  "$ cd ..", {[cur_size, parent_size | rest], min_dir_size} ->
    new_path = [cur_size + parent_size | rest]

    if cur_size >= need_to_clean and cur_size < min_dir_size do
      {new_path, cur_size}
    else
      {new_path, min_dir_size}
    end

  "$ cd " <> _dir, {path, min_dir_size} ->
    {[0 | path], min_dir_size}

  "$ ls", fs ->
    fs

  "dir " <> _, fs ->
    fs

  file_entry, {[cur_size | rest], min_dir_size} ->
    size = file_entry_size.(file_entry)
    {[cur_size + size | rest], min_dir_size}
end)