Advent of Code - Day 09

Mix.install([{:kino, github: "livebook-dev/kino"}])

kino_input = Kino.Input.textarea("Please paste your input file: ")

Part 1

input = Kino.Input.read(kino_input)

input
|> String.trim()
|> String.split("", trim: true)
|> Enum.map(&String.to_integer/1)
|> Enum.chunk_every(2, 2, [0])
|> Enum.with_index()
|> Enum.flat_map(fn {[blocks, free_space], id} -> 
  [List.duplicate(id, blocks), List.duplicate(nil, free_space)] |> List.flatten()
end)
|> then(fn disk_map ->
  compacted_disk_map = disk_map
    |> Enum.reduce_while({[], disk_map |> Enum.filter(& &1) |> Enum.reverse()}, fn val, {acc, map} ->
      if Enum.empty?(map) do
        {:halt, acc}
      else
        case val do
          nil -> {:cont, {[hd(map) | acc], tl(map)}}
          val -> {:cont, {[val | acc], List.delete_at(map, -1)}}
        end
      end
    end)

  disk_length = length(compacted_disk_map)

  compacted_disk_map
  |> Enum.with_index()
  |> Enum.reduce(0, fn {block, id}, acc ->
    acc + block * (disk_length - id - 1)
  end)
end)

Part 2

input = Kino.Input.read(kino_input)

# gave up, https://github.com/Flo0807/adventofcode/blob/main/2024/09.livemd
defmodule PlaceFinder do
  def fill_blocks(blocks, acc \\ [])
  def fill_blocks([], acc), do: List.flatten(acc)

  def fill_blocks([[first | _rest] = block | rest], acc) when first == "." do
    case find_suitable_block(rest, length(block)) do
      nil ->
        fill_blocks(rest, acc ++ [block])

      {num_block, index} ->
        extra_dots = length(block) - length(num_block)
        remaining_dots = if extra_dots > 0, do: [List.duplicate(".", extra_dots)], else: []
        new_rest = List.replace_at(rest, index, List.duplicate(".", length(num_block)))
        fill_blocks(remaining_dots ++ new_rest, acc ++ [num_block])
    end
  end

  def fill_blocks([block | rest], acc), do: fill_blocks(rest, acc ++ [block])

  defp find_suitable_block(blocks, dot_size) do
    blocks
    |> Enum.reverse()
    |> Enum.with_index()
    |> Enum.find(fn {[first | _] = list, _} ->
      first != "." &amp;&amp; length(list) <= dot_size
    end)
    |> case do
      nil -> nil
      {block, i} -> {block, length(blocks) - 1 - i}
    end
  end
end

input
|> String.trim()
|> String.split("", trim: true)
|> Enum.chunk_every(2, 2)
|> Enum.with_index()
|> Enum.flat_map(fn
  {[file, space], i} ->
    List.duplicate("#{i}", String.to_integer(file)) ++
      List.duplicate(".", String.to_integer(space))

  {[file], i} ->
    List.duplicate("#{i}", String.to_integer(file))
end)
|> Enum.chunk_by(&amp;(&amp;1 == "."))
|> Enum.flat_map(fn el -> Enum.chunk_by(el, &amp; &amp;1) end)
|> PlaceFinder.fill_blocks()
|> Enum.with_index()
|> Enum.reduce(0, fn
  {value, id}, acc when value != "." -> acc + id * String.to_integer(value)
  _, acc -> acc
end)