Day 9

Mix.install([
  {:kino, "~> 0.14.2"},
  {:kino_aoc, "~> 0.1.7"}
])

Part 1

{:ok, input} = 
  KinoAOC.download_puzzle("2024", "9", System.fetch_env!("LB_AOC_SESSION"))

input = "2333133121414131402" 
  
input = input |> String.graphemes() |> Enum.map(&String.to_integer/1)

defmodule Part1 do
  def decompress(dense_format, type, counter \\ 0, acc \\ [])
  def decompress([], _, _, acc), do: Enum.reverse(acc)
  def decompress([count | rest], :file, file_number, acc) do
    decompress(rest, :free, file_number + 1, prepend(acc, file_number, count))
  end
  def decompress([count | rest], :free, file_number, acc) do
    decompress(rest, :file, file_number, prepend(acc, ".", count))
  end

  def fill(left, right, acc \\ [])

  def fill(left = ["." | _], ["." | r_rest], acc), do: fill(left, r_rest, acc)
  def fill([match | l_rest], [match | r_rest], acc) when match != "." do
    fill(l_rest, r_rest, [match | acc], :match)
  end

  def fill(["." | l_rest], [right | r_rest], acc) do
    fill(l_rest, r_rest, [right | acc])
  end
  
  def fill(left, ["." | r_rest], acc) do
    fill(left, r_rest, acc)
  end
  
  def fill([left | l_rest], r_rest, acc) when left != "." do
    fill(l_rest, r_rest, [left | acc])
  end

  def fill([match | l_rest], [match | r_rest], acc, :match) when match != "." do
    fill(l_rest, r_rest, [match | acc], :match)
  end
  def fill(_, _, acc, :match), do: acc

  def prepend(list, value, until, count \\ 0)
  def prepend(list, value, until, count) when count < until do
    prepend([value | list], value, until, count + 1)
  end
  def prepend(list, _, _, _), do: list
end

decomp = Part1.decompress(input, :file)
fill = Part1.fill(decomp, Enum.reverse(decomp)) |> Enum.reverse()
sum = fill 
  |> Enum.with_index()
  |> Enum.reduce(0, fn {x, y}, acc -> x * y + acc end)

Part 2

defmodule Part2 do
  def decompress(dense_format, type, counter \\ 0, acc \\ [])
  def decompress([], _, _, acc), do: Enum.reverse(acc)
  def decompress([count | rest], :file, file_number, acc) do
    decompress(rest, :free, file_number + 1, prepend(acc, file_number, count))
  end
  def decompress([count | rest], :free, file_number, acc) do
    decompress(rest, :file, file_number, prepend(acc, ".", count))
  end

  def fill(left, right, acc \\ [])

  def fill(left = ["." | _], ["." | r_rest], acc), do: fill(left, r_rest, acc)
  def fill([match | l_rest], [match | r_rest], acc) when match != "." do
    fill(l_rest, r_rest, [match | acc], :match)
  end

  def fill(lfull = ["." | l_rest], rfull = [right | r_rest], acc) do
    if count(lfull) >= count(rfull) do
      fill(l_rest, r_rest, [right | acc])
    else
      fill(lfull, r_rest, acc)
    end
  end
  
  def fill(left, ["." | r_rest], acc) do
    fill(left, r_rest, acc)
  end
  
  def fill([left | l_rest], r_rest, acc) when left != "." do
    fill(l_rest, r_rest, [left | acc])
  end

  def fill([match | l_rest], [match | r_rest], acc, :match) when match != "." do
    fill(l_rest, r_rest, [match | acc], :match)
  end
  def fill(_, _, acc, :match), do: acc

  # Counts first value
  def count([value | rest]), do: count(rest, value, 1)
  def count([value | rest], value, count), do: count(rest, value, count + 1)
  def count(_, value, count) do
    IO.inspect({value, count})
    count
  end

  def prepend(list, value, until, count \\ 0)
  def prepend(list, value, until, count) when count < until do
    prepend([value | list], value, until, count + 1)
  end
  def prepend(list, _, _, _), do: list
end

result = decomp 
  |> Part2.fill(Enum.reverse(decomp)) |> Enum.reverse()