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Day 18 - Advent of Code 2023

lib/advent_of_code/2023/day-18.livemd

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Tyler Johnson
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Day 18 - Advent of Code 2023

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

Links

Input

input = Kino.Input.textarea("Please paste your input file:")
input = input |> Kino.Input.read()
"R 10 (#3180b0)\nU 8 (#017833)\nR 2 (#1b4a10)\nU 3 (#017831)\nR 11 (#4026e0)\nU 6 (#54c783)\nR 3 (#31fcc0)\nU 7 (#4e9493)\nL 6 (#5afbc2)\nU 2 (#0bd503)\nL 8 (#0915f2)\nU 6 (#0bd501)\nR 5 (#5adcb2)\nU 10 (#08ce13)\nR 6 (#358a90)\nD 10 (#55b9d3)\nR 7 (#045310)\nU 4 (#0c8861)\nR 4 (#6942a0)\nD 8 (#479e01)\nR 3 (#35d6d0)\nD 6 (#35ab11)\nR 4 (#2fd170)\nU 3 (#60ef11)\nR 6 (#58dd50)\nU 8 (#0f2651)\nL 6 (#059b50)\nU 3 (#2da143)\nR 5 (#066ee0)\nU 5 (#5b2963)\nL 6 (#527410)\nU 4 (#711c33)\nL 8 (#577010)\nU 4 (#083323)\nL 3 (#75fc72)\nD 4 (#183e23)\nL 5 (#3718d2)\nU 4 (#3569a3)\nL 5 (#0de902)\nU 3 (#570cb1)\nR 5 (#3c1cd2)\nU 3 (#570cb3)\nR 6 (#45e2c2)\nU 6 (#0b9413)\nR 5 (#50dd60)\nD 9 (#279343)\nR 9 (#5fb8e0)\nU 4 (#498903)\nR 2 (#166b20)\nU 10 (#1e2983)\nL 8 (#75fc70)\nU 2 (#1e5023)\nL 11 (#451642)\nU 3 (#4a17b3)\nL 2 (#2d0862)\nU 7 (#2d8203)\nL 11 (#2d0860)\nU 7 (#630fa3)\nL 2 (#60be02)\nU 3 (#326253)\nL 3 (#288692)\nU 4 (#46a9e3)\nL 9 (#415332)\nU 5 (#5c2991)\nR 3 (#582242)\nU 6 (#1ce2a1)\nR 5 (#15ccc2)\nU 5 (#4fe401)\nR 3 (#0b7832)\nU 9 (#791d41)\nR 5 (#0b7830)\nD 2 (#11a811)\nR 3 (#21f8a2)\nD 12 (#752373)\nR 5 (#4273f2)\nD 4 (#0bef43)\nR 6 (#472ef2)\nD 2 (#0ae933)\nR 4 (#6e8fa0)\nU 6 (#4b3fc3)\nR 11 (#1a18a0)\nU 2 (#204183)\nR 10 (#689d72)\nU 2 (#166963)\nR 6 (#200ad2)\nU 9 (#409303)\nR 3 (#5168a2)\nU 6 (#182991)\nR 7 (#00de82)\nU 4 (#41fc51)\nR 6 (#5648a0)\nU 2 (#17c011)\nR 3 (#5648a2)\nU 11 (#472561)\nR 4 (#00de80)\nU 2 (#145b81)\nR 7 (#6bad12)\nD 5 (#5e9d63)\nR 3 (#4c1952)\nD 4 (#002863)\nR 9 (#124bd2)\nD 3 (#25f571)\nR 5 (#39af72)\nU 9 (#261871)\nR 2 (#39af70)\nU 3 (#3e3d51)\nR 5 (#1ba6d2)\nU 6 (#11b181)\nR 8 (#5e0242)\nU 7 (#631bd3)\nL 8 (#1d0562)\nU 5 (#38e0e3)\nL 3 (#2052b2)\nU 9 (#423193)\nL 5 (#05ba00)\nU 7 (#3648c3)\nL 4 (#4871c0)\nU 4 (#30bdc1)\nL 8 (#421980)\nD 3 (#30bdc3)\nL 4 (#201d60)\nD 8 (#181023)\nL 4 (#18ea50)\nU 7 (#4cfb23)\nL 8 (#0d4ee2)\nU 7 (#1f53c3)\nR 7 (#118482)\nU 7 (#36b581)\nR 3 (#190502)\nU 4 (#3fc8e1)\nR 9 (#6832a2)\nU 7 (#19c913)\nR 2 (#471882)\nU 4 (#5cb553)\nR 5 (#3531d2)\nD 4 (#1f53c1)\nR 4 (#264472)\nD 6 (#5e7773)\nL 6 (#61f782)\nD 5 (#3b3223)\nR 6 (#648152)\nD 7 (#478223)\nR 6 (#1c4420)\nU 5 (#243b71)\nR 7 (#6c3910)\nU 2 (#243b73)\nR 2 (#3dfba0)\nU 12 (#19c593)\nR 3 (#77f502)\nD 11 (#381303)\nR 4 (#0cff42)\nD 3 (#1cd823)\nR 4 (#5f54b2)\nU 4 (#141391)\nR 6 (#1a7fd2)\nU 3 (#40d791)\nR 3 (#4d9772)\nU 9 (#19cab1)\nR 9 (#226420)\nU 5 (#284511)\nL 6 (#3456e2)\nU 12 (#2ff501)\nL 4 (#3456e0)\nU 4 (#3472f1)\nR 2 (#226422)\nU 5 (#018221)\nR 8 (#4abc80)\nU 4 (#6418f1)\nL 13 (#56d0e0)\nU 2 (#1d3d21)\nL 5 (#06aec0)\nU 5 (#309301)\nR 11 (#34e632)\nU 3 (#565641)\nR 2 (#7355f2)\nU 6 (#254551)\nR 6 (#097332)\nU 7 (#61be21)\nR 5 (#185f12)\nD 5 (#0883e3)\nR 5 (#4c8672)\nD 4 (#0883e1)\nR 8 (#4b20b2)\nD 6 (#2b7841)\nR 4 (#68a900)\nD 4 (#2a69f1)\nR 10 (#15f5d2)\nD 6 (#143051)\nR 3 (#40af22)\nD 12 (#789491)\nR 5 (#4c75c2)\nD 10 (#49b161)\nR 4 (#026a90)\nD 4 (#1302b3)\nR 4 (#742f40)\nD 2 (#1302b1)\nR 11 (#2c80e0)\nD 6 (#2f3d61)\nL 9 (#68a902)\nD 9 (#18e511)\nL 6 (#52a2a2)\nD 11 (#668143)\nR 6 (#3e9d32)\nD 9 (#6f5ce3)\nR 5 (#453c72)\nD 4 (#5c53d3)\nR 4 (#245842)\nD 6 (#4248f3)\nR 5 (#52f642)\nU 8 (#0a4793)\nR 5 (#275470)\nU 8 (#633e43)\nR 3 (#5b9d50)\nU 6 (#6a1b83)\nR 5 (#4ccf90)\nU 4 (#0773d3)\nR 3 (#4fe152)\nU 7 (#0ee221)\nL 4 (#1c62c2)\nD 4 (#0ee223)\nL 6 (#3c28d2)\nU 4 (#094fb3)\nL 5 (#0d5eb0)\nU 3 (#0e2413)\nR 8 (#648660)\nU 3 (#3def33)\nR 7 (#1d86d0)\nU 6 (#294523)\nR 7 (#21e280)\nD 6 (#311ab1)\nR 11 (#5d4fd0)\nD 3 (#4da171)\nR 2 (#21c892)\nD 5 (#41aa41)\nR 5 (#21c890)\nD 4 (#143b21)\nR 3 (#1e0360)\nD 10 (#405ff3)\nR 6 (#55f4f0)\nD 12 (#70c2d3)\nL 6 (#55f4f2)\nD 2 (#237ec3)\nL 4 (#2d9e90)\nD 2 (#04ff73)\nL 6 (#465980)\nD 7 (#04ff71)\nL 4 (#06e620)\nD 4 (#10c923)\nL 7 (#456d32)\nD 8 (#543f03)\nL 3 (#3c50d0)\nD 6 (#2a5f93)\nL 5 (#3c50d2)\nD 6 (#2c66a3)\nL 7 (#5acb22)\nD 11 (#15d5d3)\nL 3 (#377b02)\nU 11 (#1b8d03)\nL 5 (#1b3fe0)\nD 2 (#015fd3)\nL 2 (#134a20)\nD 7 (#1160d3)\nL 6 (#06aee2)\nU 3 (#384eb3)\nL 10 (#738212)\nU 6 (#1a6053)\nL 11 (#7a30f0)\nU 6 (#23e2e3)\nL 6 (#4d7a80)\nU 10 (#12b763)\nL 2 (#5baed0)\nU 8 (#4572e3)\nL 6 (#5ac8b0)\nD 4 (#5dec33)\nL 3 (#0fc0b0)\nD 3 (#52fb53)\nL 5 (#2b4970)\nD 11 (#25dee3)\nL 3 (#583090)\nD 7 (#2535c1)\nR 9 (#2dafb0)\nD 5 (#345101)\nR 5 (#3068d0)\nD 4 (#0a6ba1)\nR 4 (#4a6b30)\nD 3 (#72d401)\nR 12 (#1479f0)\nD 3 (#18d0e3)\nR 2 (#222b30)\nD 4 (#4dc203)\nL 10 " <> ...

Solution

defmodule Day18 do
  defdelegate parse(input), to: __MODULE__.Input

  def part1(input) do
    input
    |> parse()
    |> Enum.reduce({{0, 0}, [], 0}, &amp;make_move/2)
    |> calc_total_points()
  end

  def part2(input) do
    input
    |> parse()
    |> convert_hex_input()
    |> Enum.reduce({{0, 0}, [], 0}, &amp;make_move/2)
    |> calc_total_points()
  end

  defp make_move({dir, num, _color}, {current, list, points}) do
    next = next_vertex(current, dir, num)

    {next, [next | list], points + num}
  end

  defp next_vertex({x, y}, ?U, num), do: {x, y - num}
  defp next_vertex({x, y}, ?D, num), do: {x, y + num}
  defp next_vertex({x, y}, ?L, num), do: {x - num, y}
  defp next_vertex({x, y}, ?R, num), do: {x + num, y}

  defp calc_total_points({_, vertices, boundary_point_count}) do
    boundary_point_count + interior_point_count(vertices, boundary_point_count)
  end

  @doc """
  https://en.wikipedia.org/wiki/Pick's_theorem

  Suppose that a polygon has integer coordinates for all of its vertices.
  Let `i` be the number of integer points interior to the polygon, and let 
  `b` be the number of integer points on its boundary (including both
  vertices and points along the sides).
  Then the area `A` of this polygon is:

  A = i + b/2 - 1

  The number of interior points is then:

  i = A - b/2 + 1
  """
  def interior_point_count(vertices, b) do
    shoelace_area(vertices) - div(b, 2) + 1
  end

  # https://en.wikipedia.org/wiki/Shoelace_formula
  defp shoelace_area(loop) do
    loop
    |> Enum.chunk_every(2, 1, [hd(loop)])
    |> Enum.map(fn [{x1, y1}, {x2, y2}] ->
      x1 * y2 - x2 * y1
    end)
    |> Enum.sum()
    |> div(2)
    |> abs()
  end

  @direction %{"0" => ?R, "1" => ?D, "2" => ?L, "3" => ?U}
  defp convert_hex_input(input) do
    Enum.map(input, fn {_, _, color} ->
      {distance, dir} = String.split_at(color, 5)

      {
        @direction[dir],
        String.to_integer(distance, 16),
        nil
      }
    end)
  end

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

    def parse_line(line) do
      ~r/([UDLR]) (\d+) \(\#([0-9a-f]{6})\)/
      |> Regex.run(line, capture: :all_but_first)
      |> then(fn [dir, num, color] ->
        {
          String.to_charlist(dir) |> hd(),
          String.to_integer(num),
          color
        }
      end)
    end
  end
end
{:module, Day18, <<70, 79, 82, 49, 0, 0, 18, ...>>,
 {:module, Day18.Input, <<70, 79, 82, ...>>, {:parse_line, 1}}}

The Elves are concerned the lagoon won’t be large enough; if they follow their dig plan, how many cubic meters of lava could it hold?

Your puzzle answer was 70026.

Day18.part1(input)
70026

Convert the hexadecimal color codes into the correct instructions; if the Elves follow this new dig plan, how many cubic meters of lava could the lagoon hold?

Your puzzle answer was 68548301037382.

Day18.part2(input)
68548301037382

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 Day18Test do
  use ExUnit.Case, async: false

  setup_all do
    [
      input:
        "R 6 (#70c710)\nD 5 (#0dc571)\nL 2 (#5713f0)\nD 2 (#d2c081)\nR 2 (#59c680)\nD 2 (#411b91)\nL 5 (#8ceee2)\nU 2 (#caa173)\nL 1 (#1b58a2)\nU 2 (#caa171)\nR 2 (#7807d2)\nU 3 (#a77fa3)\nL 2 (#015232)\nU 2 (#7a21e3)"
    ]
  end

  describe "part1/1" do
    test "returns expected value", %{input: input} do
      assert Day18.part1(input) == 62
    end
  end

  describe "part2/1" do
    test "returns expected value", %{input: input} do
      assert Day18.part2(input) == 952_408_144_115
    end
  end
end

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

Randomized with seed 950624
%{total: 2, failures: 0, excluded: 0, skipped: 0}

Benchmarking

defmodule Benchmarking do
  # https://github.com/bencheeorg/benchee
  def run(input) do
    Benchee.run(
      %{
        "Part 1" => fn -> Day18.part1(input) end,
        "Part 2" => fn -> Day18.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 1.15.7
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        1.47 K      682.48 μs     ±4.01%      672.17 μs      770.24 μs
Part 2        1.15 K      872.01 μs     ±2.93%      861.71 μs      942.04 μs

Comparison: 
Part 1        1.47 K
Part 2        1.15 K - 1.28x slower +189.54 μs

Memory usage statistics:

Name           average  deviation         median         99th %
Part 1         0.66 MB     ±0.20%        0.66 MB        0.67 MB
Part 2         1.10 MB     ±0.00%        1.10 MB        1.10 MB

Comparison: 
Part 1         0.66 MB
Part 2         1.10 MB - 1.65x memory usage +0.43 MB

Reduction count statistics:

Name   Reduction count
Part 1         51.62 K
Part 2         77.67 K - 1.50x reduction count +26.05 K

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