Day 05

Part 1

[raw_stacks, raw_ops] =
  "./2022/day05input.txt"
  |> File.read!()
  |> String.split("\n\n")

clean_stacks =
  raw_stacks
  |> String.to_charlist()
  |> Enum.chunk_every(4)
  |> Enum.map(&(&1 |> to_string() |> String.trim()))

nb_stacks = clean_stacks |> List.last() |> String.to_integer()

stacks =
  clean_stacks
  |> Enum.chunk_every(nb_stacks)
  |> Enum.zip_with(& &1)
  |> Map.new(fn line ->
    [group | reversed] = Enum.reverse(line)
    values = reversed |> Enum.reverse() |> Enum.reject(&(&1 == ""))
    {group, values}
  end)

ops = String.split(raw_ops, "\n")

Enum.reduce(
  ops,
  stacks,
  fn
    "", stacks ->
      stacks

    line, stacks ->
      [_move, count_str, _from, start_pos, _to, end_pos] = String.split(line)
      count = String.to_integer(count_str)

      start_values = Map.fetch!(stacks, start_pos)
      {moved, new_start_values} = Enum.split(start_values, count)
      new_end_values = Enum.reverse(moved) ++ Map.fetch!(stacks, end_pos)

      stacks
      |> Map.put(start_pos, new_start_values)
      |> Map.put(end_pos, new_end_values)
  end
)
|> Enum.to_list()
|> Enum.sort_by(&elem(&1, 0))
|> Enum.map(fn {_group, stack} -> stack |> List.first() |> String.at(1) end)
|> Enum.join()

This is the most awful piece of code I’ve written in ages. But it works

Part 2

[raw_stacks, raw_ops] =
  "./2022/day05input.txt"
  |> File.read!()
  |> String.split("\n\n")

clean_stacks =
  raw_stacks
  |> String.to_charlist()
  |> Enum.chunk_every(4)
  |> Enum.map(&(&1 |> to_string() |> String.trim()))

nb_stacks = clean_stacks |> List.last() |> String.to_integer()

stacks =
  clean_stacks
  |> Enum.chunk_every(nb_stacks)
  |> Enum.zip_with(& &1)
  |> Map.new(fn line ->
    [group | reversed] = Enum.reverse(line)
    values = reversed |> Enum.reverse() |> Enum.reject(&(&1 == ""))
    {group, values}
  end)

ops = String.split(raw_ops, "\n")

Enum.reduce(
  ops,
  stacks,
  fn
    "", stacks ->
      stacks

    line, stacks ->
      [_move, count_str, _from, start_pos, _to, end_pos] = String.split(line)
      count = String.to_integer(count_str)

      start_values = Map.fetch!(stacks, start_pos)
      {moved, new_start_values} = Enum.split(start_values, count)
      # Removed the reverse, lol
      new_end_values = moved ++ Map.fetch!(stacks, end_pos)

      stacks
      |> Map.put(start_pos, new_start_values)
      |> Map.put(end_pos, new_end_values)
  end
)
|> Enum.to_list()
|> Enum.sort_by(&elem(&1, 0))
|> Enum.map(fn {_group, stack} -> stack |> List.first() |> String.at(1) end)
|> Enum.join()