Day 17 - Advent of Code 2023

Mix.install([
  {:heap, "~> 3.0"},
  {:kino, "~> 0.12.0"},
  {:benchee, "~> 1.2"}
])

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()

"333213136361262336321612214531777457112145343436646554277834586842636477377358665483232322865545123271135255712112742775561145666154365233356\n625436214642112116663631316165754345156613447614784645884723775385422237785533457846422687888517441575665644164125345724771731422533345336535\n135464262413363523172353673663343124614327663325483447348582478365458326464522365884857228745883344645545337271265517463212456153534241544452\n463341164253235233654257664712176156221273446338438725387868466637872246443458373458772474446735864427171225417624722447465614145334226531133\n612123231364647651775663426212224226114337776577776736788424832776656343782563357835523563646643373362516426762263641757743221457544513132115\n554121446241214313746711736452662635625733462823288665545675563668763743787742653833765545345747825838821335355445434347415641445636564324243\n224451135242133732146576324716743753368865727642288276285674826268356773857358774272262757346428753268886423252537566456457145362241413235356\n312115633663242411233636615741633726487283228864835444425576777233878745223464452866553565685646725656653473162633463643521135773411433452466\n542364224173757771326524416535552277757354762743288837354468764353627364676267546484532727724264832675772357663444464333544311464653635434155\n644453415415675332722151756256718248247685882878285324462473375646475283722538546752748236463677656374757244824312452134314757122175246666133\n553335516731473766365715331215568572352758878273527332573426865584372534367686638785426548725847452264452655432363227522743746771746731616324\n133445474224722676227554462116647666753275526734788533873228633423522662378822462553685245662683348523576827224635133441463776656147576542321\n262263545476415133716375434754684868667682745356337755425335477366862483227738582326352468542752785886234837282845863613725264761734336443244\n114557561615633115446342258245858844385456266756554434328822765476533686573637497788623453646223225852468238675466763313713633227154741356245\n611315162633241542646131578684535533767564585652735786467776834489896877967363837453335767245825426445885342673428236331451157547442775237312\n362261614652576557153353266488324456657568285858237439538887578466544663574533349347999664436466843472663827648852522875316714732344324217372\n154236775775512321522263368636678482445745255477872966786867669355994753645973978496654594795457367226453428858886655252654623377164654233436\n462622424671674313226637785458826766472883676833993634453836356375787779937773696649358983467446647337585265887587723374463642735172144752645\n256461325176535257663462355464575334764872223438763949469848778946443559566434444799354636443886736785674266463345527548557615613664272723332\n624227517633531434243827827654636862345763525366656758486948446474677985365493464466378853868458497378656656647884675348243277163765174172612\n642426252112436471458742474775766555755482666556764666989755347483839876866543593833948554547649543695673778734785343556567234476436622452236\n472761551511731356577488843522288387648575847749585654676577859987674545338478446453935695888655834749368252388424646347784477427672675234731\n747257136413274266658434523648663224583865945533979664865739647394863547663534658684836947849398659354975525423267856334772333414472751271125\n574343547662773544664738635233783383586446637996489896655677988659366366569546668595949965836367778345574626644234463758638787822267745754521\n367475241771674622685256576755377256694657754777544899383684634438534485979934747656784795398385666575337783432384738285554737675522715746365\n256367447543715652882652564564844549667487979647384545688783886347534748746799385454464568597377867697868876544676868477782387732724561552121\n261235663177628353884845384445766258763957538398695337944456734653958794684775489984866453396736953989445799737336434633265843536845722326147\n431276435456537534853737352526378373785887936397348334479754963636988696675746463374338676858375353484947593688636237753457284385777117617624\n421367347552372223365324757658483977886994994547997755837953398686686495795587856558739768889585363493453579446427556683" <> ...

Solution

defmodule Day17 do
  defdelegate parse(input), to: __MODULE__.Input

  def part1(input) do
    {grid, queue, seen} = setup(input)

    shortest_path(grid, queue, seen, :part1)
  end

  def part2(input) do
    {grid, queue, seen} = setup(input)

    shortest_path(grid, queue, seen, :part2)
  end

  defp setup(input) do
    {
      parse(input),
      [{0, {0, 0, :R, 0}}] |> Enum.into(Heap.min()),
      MapSet.new([])
    }
  end

  defp shortest_path(grid, queue, seen, part) do
    {h, tail} = Heap.split(queue)

    neighbors(h, grid, part)
    |> Enum.reject(&MapSet.member?(seen, elem(&1, 1)))
    |> Enum.reduce_while({tail, seen}, fn next, {queue, seen} ->
      {distance, {x, y, _, moves}} = next

      if (part != :part2 or moves >= 4) and x == grid.max_x and y == grid.max_y do
        {:halt, distance}
      else
        {:cont, {Heap.push(queue, next), MapSet.put(seen, elem(next, 1))}}
      end
    end)
    |> then(fn
      {queue, seen} ->
        shortest_path(grid, queue, seen, part)

      distance when is_integer(distance) ->
        distance
    end)
  end

  defp neighbors({distance, {x, y, dir, moves}}, grid, part) do
    [:U, :D, :L, :R]
    |> part_filters(dir, moves, part)
    |> Enum.reject(fn
      :U -> dir == :D
      :D -> dir == :U
      :L -> dir == :R
      :R -> dir == :L
    end)
    |> Enum.map(fn
      :U -> {x, y - 1, :U}
      :D -> {x, y + 1, :D}
      :L -> {x - 1, y, :L}
      :R -> {x + 1, y, :R}
    end)
    |> Enum.reject(fn {x, y, _} -> grid[{x, y}] |> is_nil() end)
    |> Enum.map(fn
      {x, y, ^dir} -> {x, y, dir, moves + 1}
      next -> Tuple.append(next, 1)
    end)
    |> Enum.map(fn {x, y, _, _} = next ->
      {distance + grid[{x, y}], next}
    end)
  end

  defp part_filters(directions, curr_dir, moves, :part1) do
    directions
    |> Enum.reject(&(moves == 3 and &1 == curr_dir))
  end

  defp part_filters(directions, curr_dir, moves, :part2) do
    directions
    |> Enum.reject(&amp;(moves < 4 and &amp;1 != curr_dir))
    |> Enum.reject(&amp;(moves == 10 and &amp;1 == curr_dir))
  end

  defmodule Input do
    def parse(input) do
      input
      |> String.splitter("\n", trim: true)
      |> Stream.with_index()
      |> Enum.reduce(%{}, &amp;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 - 48)
      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, Day17, <<70, 79, 82, 49, 0, 0, 26, ...>>,
 {:module, Day17.Input, <<70, 79, 82, ...>>, {:add_max_xy, 1}}}

Directing the crucible from the lava pool to the machine parts factory, but not moving more than three consecutive blocks in the same direction, what is the least heat loss it can incur?

Your puzzle answer was 1128.

Day17.part1(input)

1128

Directing the ultra crucible from the lava pool to the machine parts factory, what is the least heat loss it can incur?

Your puzzle answer was 1268.

Day17.part2(input)

1268

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 Day17Test do
  use ExUnit.Case, async: false

  setup_all do
    [
      input1:
        "2413432311323\n3215453535623\n3255245654254\n3446585845452\n4546657867536\n1438598798454\n4457876987766\n3637877979653\n4654967986887\n4564679986453\n1224686865563\n2546548887735\n4322674655533",
      input2: "111111111111\n999999999991\n999999999991\n999999999991\n999999999991"
    ]
  end

  describe "part1/1" do
    test "returns expected value", %{input1: input1} do
      assert Day17.part1(input1) == 102
    end
  end

  describe "part2/1" do
    test "returns expected value", %{input1: input1, input2: input2} do
      assert Day17.part2(input1) == 94
      assert Day17.part2(input2) == 71
    end
  end
end

ExUnit.run()

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

Randomized with seed 540641

%{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 -> Day17.part1(input) end,
        "Part 2" => fn -> Day17.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
Number of Available Cores: 8
Available memory: 8 GB
Elixir 1.15.7
Erlang 26.1.1

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          2.63         0.38 s     ±7.43%         0.37 s         0.44 s
Part 2          0.66         1.51 s     ±1.77%         1.50 s         1.54 s

Comparison: 
Part 1          2.63
Part 2          0.66 - 3.96x slower +1.13 s

Memory usage statistics:

Name      Memory usage
Part 1         0.57 GB
Part 2         1.90 GB - 3.34x memory usage +1.33 GB

**All measurements for memory usage were the same**

Reduction count statistics:

Name           average  deviation         median         99th %
Part 1         45.98 M     ±0.01%        45.98 M        45.99 M
Part 2        151.71 M     ±0.01%       151.71 M       151.71 M

Comparison: 
Part 1         45.98 M
Part 2        151.71 M - 3.30x reduction count +105.72 M

nil