Day 13 - 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()

"#.###.##..#....\n.#.###.....####\n...##...###.##.\n...######..#..#\n##.#..#.##..##.\n.#.##..#....##.\n##..##.#...####\n.####..##.#####\n#.####.#....##.\n..#.###.#..#..#\n##...####...##.\n##...####...##.\n..#.###.#..#..#\n#.###..#....##.\n.####..##.#####\n\n##..#.#......#..#\n.....#..#.#######\n...########...##.\n..#.#.#.###...##.\n..#.#..#.#.#.#..#\n..##...#.##.#.##.\n###.####..##.#...\n....#..#.#..#.##.\n....#.###..##....\n..##.#..##.######\n...##..#.#.##....\n...#.#..#........\n###....##..######\n..#...##..##.#..#\n..#.......#...##.\n\n#####.###\n.#.###..#\n##...##.#\n....###.#\n....###.#\n##...##.#\n.#.###..#\n#####.###\n..##.#.##\n###...##.\n.##.#.###\n.##.#.#.#\n###...##.\n\n..###...#####\n#######..#..#\n########.#..#\n..###...#####\n##.###..#####\n#.....###.##.\n#..###..##..#\n.#.#.##...##.\n.#.##########\n..###.###.##.\n####..#.#....\n##.##.....##.\n###...##.....\n...#.#.##....\n.##..#.#.#..#\n\n#......#...\n.#.#.##....\n##..####.##\n...##....##\n..#...##...\n#..#.......\n##..#.#..##\n###..#.####\n###..#.#.##\n\n..#......#...\n###.####.####\n.#..#..#.##..\n.#..#..#..#..\n##..####..###\n##..####..###\n.....##......\n.###.##.###..\n##..####..###\n#.########.##\n.##......##..\n.#..#..#..#..\n#...####...##\n\n#....##.#..#.##\n.#..#.##.####.#\n.#..#.##.####.#\n#....##.#..####\n#.##.#..#.####.\n......#..#....#\n.#..#...#..##.#\n.#..#.###.##.##\n..##...##...#.#\n......#.####.#.\n#.##.#..#......\n..##...###.#.#.\n......#..##.#.#\n\n..##.######\n##.....#..#\n..#.###.##.\n#.###..####\n.##.#..#..#\n.##....#..#\n#.###..####\n\n...#.####.#\n##.#..##..#\n##.........\n..##..##..#\n##..#....#.\n##....##...\n..#........\n##..#.##.#.\n...#......#\n...#.###..#\n...########\n####..##..#\n..#.##..##.\n###..####..\n..#.######.\n\n##.....###...\n##.....###...\n##.##.####.##\n###..###.##..\n........#..#.\n#.#..#.#..##.\n##.##.###..#.\n\n...##.####.#.#.\n..####.#...#...\n.....##.#.#..##\n##.....###.#.#.\n######.###.#...\n##.##....#.####\n...#.####..####\n..###....##.##.\n..###..#...#..#\n..###..##..#..#\n..###....##.##.\n...#.####..####\n##.##....#.####\n######.###.#...\n##.....###.#.#.\n\n##.#####.####..\n..#.##..#.##.#.\n..#.########...\n###.###.###....\n...#####.##.#..\n##.#..#..#...#.\n...##....#..#..\n##..##...##.##.\n##..##..####.#.\n##....#.#.##..#\n###...#.#.##..#\n##..##..####.#.\n##..##...##.##.\n\n...#.##.##.##.#..\n#....#..##..#....\n.#..#.##..##.#..#\n.#..#.##..##.#..#\n#....#..##..#....\n...#.##.##.##.#..\n####.##....##.###\n.#.##........##.#\n######.#..#.#####\n#.##...#..#...#..\n.#.#....##....#.#\n....#.#.##.#.#...\n##..###.##.###..#\n#.#.#.#....#.#.#.\n.######....######\n\n..#..###.\n..#.#.###\n..#...###\n.##....##\n....#.#.#\n####.##..\n####.##..\n....#.#.#\n.##....##\n..#...###\n..#.#.###\n\n....##.##\n#.##.....\n###....#.\n###....#.\n#.##.....\n....##.##\n#.#..####\n#.#.....#\n.##.#.#.#\n##...#.#.\n##...#.#.\n.#..#.#.#\n#.#.....#\n#.#..####\n....##.##\n#.##.....\n###....#.\n\n###.#........\n#.#.#.#.##.#.\n##.##.#.##.#.\n..##.#.#..#.#\n.##...#....#.\n.#...##.##.##\n.#...##.##.##\n.##...#....#.\n..##.#.#..#.#\n##.##.#.##.#.\n#.#...#.##.#.\n###.#........\n#.....#.##.#.\n\n#.##..###..####\n.##...#..###..#\n.##...#..#.#..#\n.#.######..##.#\n#....##.###.###\n.###..#.##.##..\n...#.#.##..#...\n#.........###.#\n###.#.....##..#\n###.#.....##..#\n#.........###.#\n...#.#.##..#...\n.###..#.##.##..\n#....##.###.###\n.#.######..##.#\n.##...#..#.#..#\n.##...#..###..#\n\n.....######....\n..#.#..##..#.#.\n##.#........#.#\n###....##....##\n##.....##.....#\n..############.\n..#...#..#.....\n\n##...##\n#..###.\n#...#.#\n#...#.#\n#..###.\n##...##\n###.##.\n#.#..##\n..##..#\n.#..#..\n#.##..#\n#....#.\n#....#.\n#.#...#\n.#..#..\n\n#..##.###..\n.##....#.#.\n......##.#.\n#..#.###.##\n######.....\n######.....\n#..#.######\n\n...##..##.#..###.\n..#.#..#.#....##.\n####.##.####....#\n.##.#..#.##..#..#\n.#.#....#.#...###\n##..####..###..#.\n##..####..###..#.\n.#.#....#.#...###\n.##.#..#.##..#..#\n####.##.####....#\n..#.#..#.#....##.\n\n####.#...\n...#.####\n##...##..\n###.#....\n..#.#.#..\n###....##\n####.####\n..##.#..#\n##.###..#\n.#.#..#.#\n###.###..\n###.#.###\n######.#.\n..#.#.###\n####....#\n####....#\n..#.#.###\n\n#..##..##..##..##\n##.#....####....#\n##.######..######\n...######..######\n#..#.##.#..#.##.#\n#####.########.##\n###..##..##..##..\n\n###....####\n####...##.#\n##.##.##..#\n####..##..#\n##.##.#.##.\n##.###.####\n####.######\n####.#..##.\n....." <> ...

Solution

defmodule Day13 do
  defdelegate parse(input), to: __MODULE__.Input

  def part1(input) do
    input
    |> parse()
    |> Stream.map(&find_reflection/1)
    |> Stream.map(fn
      {:x, x} -> x
      {:y, y} -> y * 100
    end)
    |> Enum.sum()
  end

  def part2(input) do
    input
    |> parse()
    |> Stream.map(&find_smudge_reflection/1)
    |> Stream.map(fn
      {:x, x} -> x
      {:y, y} -> y * 100
    end)
    |> Enum.sum()
  end

  defp find_smudge_reflection(grid) do
    reflection = find_reflection(grid)

    Enum.find_value(grid, fn
      {{x, y}, ?.} ->
        find_reflection(Map.put(grid, {x, y}, ?#), reflection)

      {{x, y}, ?#} ->
        find_reflection(Map.put(grid, {x, y}, ?.), reflection)

      _ ->
        nil
    end)
  end

  defp find_reflection(grid, reflection \\ nil) do
    find_reflection(:x, grid, reflection) || find_reflection(:y, grid, reflection)
  end

  defp find_reflection(:x, grid, reflection) do
    Enum.find_value(1..grid.max_x, fn x ->
      if reflection != {:x, x} and is_reflection?(:x, x, grid) do
        {:x, x}
      end
    end)
  end

  defp find_reflection(:y, grid, reflection) do
    Enum.find_value(1..grid.max_y, fn y ->
      if reflection != {:y, y} and is_reflection?(:y, y, grid) do
        {:y, y}
      end
    end)
  end

  @doc """
      ><
  #.##..##.
  ..#.##.#.
  ##......#
  ##......#
  ..#.##.#.
  ..##..##.
  #.#.##.#.
      ><

  When x == 5, for every y, we want to check if:
  - {4, y} == {5, y}
  - {3, y} == {6, y}
  - {2, y} == {7, y}
  - {1, y} == {8, y}
  - {0, y} == {9, y} (OFF GRID! this is ok)

  """
  def is_reflection?(:x, line_x, grid) do
    Enum.all?(0..grid.max_y, fn y ->
      Enum.all?((line_x - 1)..0, fn x ->
        a = grid[{x, y}]
        b = grid[{2 * line_x - x - 1, y}]
        is_nil(a) or is_nil(b) or a == b
      end)
    end)
  end

  def is_reflection?(:y, line_y, grid) do
    Enum.all?(0..grid.max_x, fn x ->
      Enum.all?((line_y - 1)..0, fn y ->
        a = grid[{x, y}]
        b = grid[{x, 2 * line_y - y - 1}]
        is_nil(a) or is_nil(b) or a == b
      end)
    end)
  end

  defmodule Input do
    def parse(input) when is_binary(input) do
      input
      |> String.splitter("\n\n", trim: true)
      |> Stream.map(&amp;parse_grid/1)
    end

    def parse(input) do
      Stream.map(input, &amp;parse_grid/1)
    end

    def parse_grid(input) do
      input
      |> String.split("\n", trim: true)
      |> Enum.with_index()
      |> Enum.reduce(%{}, &amp;parse_line/2)
      |> add_max_xy()
    end

    def 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(&amp;elem(&amp;1, 0)) |> Enum.max()
      y = Map.keys(grid) |> Enum.map(&amp;elem(&amp;1, 1)) |> Enum.max()

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

{:module, Day13, <<70, 79, 82, 49, 0, 0, 24, ...>>,
 {:module, Day13.Input, <<70, 79, 82, ...>>, {:add_max_xy, 1}}}

Find the line of reflection in each of the patterns in your notes. What number do you get after summarizing all of your notes?

Your puzzle answer was 34918.

Day13.part1(input)

34918

In each pattern, fix the smudge and find the different line of reflection. What number do you get after summarizing the new reflection line in each pattern in your notes?

Your puzzle answer was 33054.

Day13.part2(input)

33054

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 Day13Test do
  use ExUnit.Case, async: false

  setup_all do
    [
      input:
        "#.##..##.\n..#.##.#.\n##......#\n##......#\n..#.##.#.\n..##..##.\n#.#.##.#.\n\n#...##..#\n#....#..#\n..##..###\n#####.##.\n#####.##.\n..##..###\n#....#..#"
    ]
  end

  describe "part1/1" do
    test "returns expected value", %{input: input} do
      assert Day13.part1(input) == 405
    end
  end

  describe "part2/1" do
    test "returns expected value", %{input: input} do
      assert Day13.part2(input) == 400
    end
  end
end

ExUnit.run()

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

Randomized with seed 648000

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

Benchmarking

# https://github.com/bencheeorg/benchee
Benchee.run(
  %{
    "Part 1" => fn -> Day13.part1(input) end,
    "Part 2" => fn -> Day13.part2(input) end
  },
  memory_time: 2,
  reduction_time: 2
)

nil

Warning: the benchmark Part 1 is using an evaluated function.
  Evaluated functions perform slower than compiled functions.
  You can move the Benchee caller to a function in a module and invoke `Mod.fun()` instead.
  Alternatively, you can move the benchmark into a benchmark.exs file and run mix run benchmark.exs

Warning: the benchmark Part 2 is using an evaluated function.
  Evaluated functions perform slower than compiled functions.
  You can move the Benchee caller to a function in a module and invoke `Mod.fun()` instead.
  Alternatively, you can move the benchmark into a benchmark.exs file and run mix run benchmark.exs

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        247.11        4.05 ms     ±2.01%        4.04 ms        4.29 ms
Part 2         14.05       71.17 ms     ±0.93%       71.00 ms       74.56 ms

Comparison: 
Part 1        247.11
Part 2         14.05 - 17.59x slower +67.12 ms

Memory usage statistics:

Name           average  deviation         median         99th %
Part 1         7.12 MB     ±0.06%        7.12 MB        7.13 MB
Part 2        89.13 MB     ±0.00%       89.13 MB       89.14 MB

Comparison: 
Part 1         7.12 MB
Part 2        89.13 MB - 12.51x memory usage +82.01 MB

Reduction count statistics:

Name   Reduction count
Part 1          0.44 M
Part 2          9.67 M - 22.19x reduction count +9.23 M

**All measurements for reduction count were the same**

nil