Day 14 - Advent of Code 2023

Mix.install([:kino, :benchee])

Links

• Advent of Code (AoC)
• AoC Puzzle Input
• tylerj GitHub - Livebook

Input

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

input = input |> Kino.Input.read()

".....O..#....O.O.....OO#...#.....#...........O#..OO...#O##..#.....#...O.OO...#.O......OO#...OO...O..\nOOO....#O.#..O#.#.OO...OO..O##...O.....O.O...#.O.......OOO.O...#.....#.#.O....O.O.....#...#.OOOO.O..\n...O..#...#O..#......O#.......#..O##O.#....##......O.O...O..#O.O..##..#..#O......##...OO.#.O#..O...#\n.O..#...##O..#....#...O.O...#........O.O..#...O..#O.O.....#O...OO.#....O..O....OO##OO#...O#.O#...#.#\n#.O......O.#.O..OO.O..#....#.OO....#.#..#..O#.O....OO......#.##O...#.OO........O..OO...OOO#O.#O#.O.#\n...##.O.#O.O.##.#..O....#.#..#.OO.O...#....#.O..O#O.O.O..O...O.O..##...O#..#.......O.O......#O.#O...\n.O.O..O..O#.O.O..O.O..O..O..............#...O#O#.O.#.##..........##O....O.O...........O..O..O#...#..\n...#O.O.OO#..O..#.#...#O...O..#...#.........O...#OO#...#.O#....O...##..O...O.#O#.O#...O.O...#OO.O#..\n...##.##.O...O..#..#O.O.O...O.##..#.#.O..OO.O......OO..#..O.O..#..#.......O..O.....OO.OOO.O..O..#O.#\n....#O.O...#OO..O.O............O.....#O..#O#...#.........O.O..O...OO....#..O..##.O..####O#O.#.......\n.OOO.......##..O..#O.OO.##.....O....#..OO.#O.......OO..........OO..O..O#...#..O..##.O........#....O.\n....#.O#...#OO..............O..O.O...O...O...O....O###....O.#OO...O#.OO.#...#.#.##.....O...........O\n.......#O##..#......#.O.#.......O#.#.O#O#..#.#...O.....O..O#..O..#.O#....O..#.......O..O..#O........\nO..O.#.O...#....##...#.....O..#.#......O..#O..#.OO..O.##.........O#O.#....#..#.###OOOO..#OO.#O.O.O#.\n...O##O.#.............#..O.O....O#.....#OO...OOO......O#.O...#O#.#..#....O..#.#..O..#.O...OO.....O..\n...O......#..O.#.#..##....O..#....#..O.#.......#..O...##O.O.......#..O.OO..O..........O....##.....#.\n........#O##..O....#....#.....O...O.O.O.OO..O........#..#.O.........O.....O..O.O..#O.O...O...#..##..\n.O.#.....O.O.#..##O#.....#.#..O......O..##.#.#....##...O...OO.#..........OO.#O#OOO..#....#.#...O.#..\n....#...#.OO....#..OO#.#OO.O....OO..#..O....OO.......##.##O####O.O.O#..#....O.O......O.....#.O..O...\n.O#O#........O.#...O#O..#O...O.#..#.#..O#........O###..O..#...#..O.##..#............O.......O..O....\n........#.O.....O...O.....##.....##.#.#.#....OO####.#..O#....#O...#.O#..O.O.#.O......O..#..O.....O..\n..O#..##O.OOOO...OO....OO#.#.O.....#.#......#...#OO#...####O#....O...O.O.O.O#....O.##OO#..O.#.O..##.\n.##...............#.O#OO.#.......#...#O.#.OOO#.O...#....#....O#..O.#..O...O#...#..O#.O#O#........OO#\n...#......##...#.#O..O......O#O.O..OOO..O##....#....O.#..O....#........OO#.#...#.O#..O....O.O##..O#.\n.OO......O.....O...##..#...#....O.#....O....O...........OO.#.#..#...#.O#O.#.#......#.O......O.O#.#.#\nO.O....#O...##.O..#O.O...#...O.......O.OO...O.O#.....#..#.O#.....O.O...........O.....O...O.....#....\n.#O#..O....O.......#..OOOO.....O.....####...#.......O...O#O...O..#..#...##.#.....#....O....#...##...\n........O.O#OO#..#.O.....#.OOO......OO#.#.....O.#..#O.........#OOO......O..#......O..##....#O....#.#\n..O..#O.....##..#.OO..O..........OO..O...#.##O.#.#..O.O#.#.#......OOO......#..O..#.O....O#...OO#....\n...#.OOO.O......O#O...O.O.OO....OO#.....O.O.O#.....O##.OO......#......OOO#O.OO.O#...#.....O....OO...\n...#.#O..O...##.#.###.O.#...#.#....O.OO...O.O.O.O...#.#.O....#OO#.OO...#O...#O...OO.O..O..O....O..O#\n.##.O......#.##.....O...OO#...O.....O..#.....O.........#....O..#....O.####......#...#........O#..OO.\n.#.#.O.#.O#..OO.#....O...#.O...O..#.O.....#OO....#.O.O.O......OO...#.#.O#O#OO.#O.O.....O.........#..\n..#.#..O...#..#.....OO.#O...O#...OO.O...O#....##O....#.#...OO.#.....#.O#.....O.....O...#.#O.....#...\n.O..OO#.#OO...O..#..........OO.............##..####...#.O....O...#.#...O#..O.O..OO.#....OOO..#...OO.\n#...#....#.........OOOO....OO....O#O..........#..O#..O...#.OOO.....OO.......OO.##...O.#....OOO...##.\n#.........#OO#.O.#..##.#.##O...#...OO....O#O......#.......O.O...#O...O.O.#O##O#..O....O#.#......O.#.\n...O..O#..#...##..O....O..O......O.O#...OO.......##......OO..#.O....#.##O.OO....#.O.#.OO..O....O.#..\n.O..O.#.O.#............O....#....#....#.#.....#...OO#...OO.##OO.#..#....#....#.O#.OO#.#.O.O#..O.....\n.OO#O...#.#......O...#...O##.O....O#...O..O..O..O.#O..#..###OO..#..O##O.#.O...O#O...OO.O..#.#O#..#.#\n#..OOOO...OOO.O..#O...OO##....O#..OO...O.O.#....#O#O...." <> ...

Solution

defmodule Day14 do
  defdelegate parse(input), to: __MODULE__.Input
  alias __MODULE__.Cache

  def part1(input) do
    input
    |> parse()
    |> roll(:north)
    |> calc_load()
  end

  def part2(input) do
    input
    |> parse()
    |> roll_cycle_loop()
  end

  defp calc_load(grid) do
    Enum.reduce(grid.max_y..0, 0, fn y, total ->
      num_rounded = Enum.count(0..grid.max_x, &(grid[{&1, y}] == ?O))

      total + num_rounded * (grid.max_y + 1 - y)
    end)
  end

  defp roll_cycle_loop(grid) do
    {:ok, cache} = Cache.start_link([])
    Cache.put(cache, string_grid(grid), 0)

    roll_cycle_loop(grid, cache, 0)
  end

  defp roll_cycle_loop(grid, cache, count) do
    new_grid = roll_cycle(grid)
    grid_key = string_grid(new_grid)

    case Cache.get(cache, grid_key) do
      nil ->
        Cache.put(cache, grid_key, count + 1)
        Cache.put(cache, count + 1, calc_load(new_grid))
        roll_cycle_loop(new_grid, cache, count + 1)

      value ->
        lookup_index = value + rem(1_000_000_000 - value, count - value + 1)
        Cache.get(cache, lookup_index)
    end
  end

  defp roll_cycle(grid) do
    grid
    |> roll(:north)
    |> roll(:west)
    |> roll(:south)
    |> roll(:east)
  end

  defp roll(grid, :north) do
    roll(grid, :north, 1..grid.max_y, 0..grid.max_x, fn y, x -> {x, y} end)
  end

  defp roll(grid, :south) do
    roll(grid, :south, (grid.max_y - 1)..0, 0..grid.max_x, fn y, x -> {x, y} end)
  end

  defp roll(grid, :west) do
    roll(grid, :west, 1..grid.max_x, 0..grid.max_y, fn x, y -> {x, y} end)
  end

  defp roll(grid, :east) do
    roll(grid, :east, (grid.max_x - 1)..0, 0..grid.max_y, fn x, y -> {x, y} end)
  end

  defp roll(grid, direction, range1, range2, xy_fun) do
    range1
    |> Enum.reduce(grid, fn a, acc ->
      range2
      |> Enum.reduce(acc, fn b, acc ->
        xy = xy_fun.(a, b)

        case acc[xy] do
          ?O ->
            new_xy = find_resting_xy(xy, acc, direction)

            acc
            |> Map.put(xy, ?.)
            |> Map.put(new_xy, ?O)

          _ ->
            acc
        end
      end)
    end)
  end

  defp find_resting_xy({x, y}, grid, :north) do
    {
      x,
      Enum.find(y..0, &(grid[{x, &1 - 1}] != ?.))
    }
  end

  defp find_resting_xy({x, y}, grid, :south) do
    {
      x,
      Enum.find(y..grid.max_y, &(grid[{x, &1 + 1}] != ?.))
    }
  end

  defp find_resting_xy({x, y}, grid, :west) do
    {
      Enum.find(x..0, &(grid[{&1 - 1, y}] != ?.)),
      y
    }
  end

  defp find_resting_xy({x, y}, grid, :east) do
    {
      Enum.find(x..grid.max_x, &(grid[{&1 + 1, y}] != ?.)),
      y
    }
  end

  def string_grid(grid) do
    grid
    |> string_rows()
    |> to_string()
  end

  def string_rows(grid) do
    0..grid.max_y
    |> Enum.map(fn y ->
      0..grid.max_x
      |> Enum.map(fn x -> grid[{x, y}] end)
      |> to_string()
    end)
  end

  def print_grid(grid, label) do
    IO.puts(label)
    grid |> string_rows() |> Enum.each(&IO.puts/1)
    grid
  end

  defmodule Cache do
    use Agent

    def start_link(_opts) do
      Agent.start_link(fn -> %{} end)
    end

    def get(cache, key) do
      Agent.get(cache, &Map.get(&1, key))
    end

    def put(cache, key, value) do
      Agent.update(cache, &Map.put(&1, key, value))
    end
  end

  defmodule Input do
    def parse(input) do
      input
      |> String.splitter("\n", trim: true)
      |> Stream.with_index()
      |> Enum.reduce(%{}, &parse_line/2)
      |> add_max_xy()
    end

    defp parse_line({line, row}, grid) do
      line
      |> String.to_charlist()
      |> Enum.with_index()
      |> Enum.reduce(grid, fn {char, col}, acc ->
        Map.put(acc, {col, row}, char)
      end)
    end

    defp add_max_xy(grid) do
      x = Map.keys(grid) |> Enum.map(&elem(&1, 0)) |> Enum.max()
      y = Map.keys(grid) |> Enum.map(&elem(&1, 1)) |> Enum.max()

      Map.merge(grid, %{max_x: x, max_y: y})
    end
  end
end

{:module, Day14, <<70, 79, 82, 49, 0, 0, 35, ...>>,
 {:module, Day14.Input, <<70, 79, 82, ...>>, {:add_max_xy, 1}}}

Tilt the platform so that the rounded rocks all roll north. Afterward, what is the total load on the north support beams?

Your puzzle answer was 103614.

Day14.part1(input)

103614

Run the spin cycle for 1000000000 cycles. Afterward, what is the total load on the north support beams?

Your puzzle answer was 83790.

Day14.part2(input)

83790

Both parts of this puzzle are complete! They provide two gold stars: **

At this point, you should return to your Advent calendar and try another puzzle.

If you still want to see it, you can get your puzzle input.

Tests

ExUnit.start(auto_run: false)

defmodule Day14Test do
  use ExUnit.Case, async: false

  setup_all do
    [
      input:
        "O....#....\nO.OO#....#\n.....##...\nOO.#O....O\n.O.....O#.\nO.#..O.#.#\n..O..#O..O\n.......O..\n#....###..\n#OO..#...."
    ]
  end

  describe "part1/1" do
    test "returns expected value", %{input: input} do
      assert Day14.part1(input) == 136
    end
  end

  describe "part2/1" do
    test "returns expected value", %{input: input} do
      assert Day14.part2(input) == 64
    end
  end
end

ExUnit.run()

..
Finished in 0.00 seconds (0.00s async, 0.00s sync)
2 tests, 0 failures

Randomized with seed 811435

%{total: 2, failures: 0, excluded: 0, skipped: 0}

Benchmarking

defmodule Benchmarking do
  def run(input) do
    Benchee.run(
      %{
        "Part 1" => fn -> Day14.part1(input) end,
        "Part 2" => fn -> Day14.part2(input) end
      },
      memory_time: 2,
      reduction_time: 2
    )

    nil
  end
end

{:module, Benchmarking, <<70, 79, 82, 49, 0, 0, 7, ...>>, {:run, 1}}

Benchmarking.run(input)

Operating System: macOS
CPU Information: Apple M1 Pro
Number of Available Cores: 10
Available memory: 32 GB
Elixir 1.15.6
Erlang 26.1

Benchmark suite executing with the following configuration:
warmup: 2 s
time: 5 s
memory time: 2 s
reduction time: 2 s
parallel: 1
inputs: none specified
Estimated total run time: 22 s

Benchmarking Part 1 ...
Benchmarking Part 2 ...

Name             ips        average  deviation         median         99th %
Part 1        198.84      0.00503 s     ±7.26%      0.00493 s      0.00598 s
Part 2          0.59         1.70 s     ±6.80%         1.70 s         1.80 s

Comparison: 
Part 1        198.84
Part 2          0.59 - 337.26x slower +1.69 s

Memory usage statistics:

Name           average  deviation         median         99th %
Part 1      0.00763 GB     ±0.01%     0.00763 GB     0.00763 GB
Part 2         2.01 GB     ±0.00%        2.01 GB        2.01 GB

Comparison: 
Part 1      0.00763 GB
Part 2         2.01 GB - 262.92x memory usage +2.00 GB

Reduction count statistics:

Name           average  deviation         median         99th %
Part 1          0.45 M     ±0.00%         0.45 M         0.45 M
Part 2        156.09 M     ±0.00%       156.09 M       156.09 M

Comparison: 
Part 1          0.45 M
Part 2        156.09 M - 348.48x reduction count +155.64 M

nil