Day 24 - Advent of Code 2022
Mix.install([:kino, :benchee]):ok
Links
Prompt
--- Day 24: Blizzard Basin ---
With everything replanted for next year (and with elephants and monkeys to tend the grove), you and the Elves leave for the extraction point.
Partway up the mountain that shields the grove is a flat, open area that serves as the extraction point. It's a bit of a climb, but nothing the expedition can't handle.
At least, that would normally be true; now that the mountain is covered in snow, things have become more difficult than the Elves are used to.
As the expedition reaches a valley that must be traversed to reach the extraction site, you find that strong, turbulent winds are pushing small blizzards of snow and sharp ice around the valley. It's a good thing everyone packed warm clothes! To make it across safely, you'll need to find a way to avoid them.
Fortunately, it's easy to see all of this from the entrance to the valley, so you make a map of the valley and the blizzards (your puzzle input). For example:
#.#####
#.....#
#>....#
#.....#
#...v.#
#.....#
#####.#
The walls of the valley are drawn as #; everything else is ground. Clear ground - where there is currently no blizzard - is drawn as .. Otherwise, blizzards are drawn with an arrow indicating their direction of motion: up (^), down (v), left (<), or right (>).
The above map includes two blizzards, one moving right (>) and one moving down (v). In one minute, each blizzard moves one position in the direction it is pointing:
#.#####
#.....#
#.>...#
#.....#
#.....#
#...v.#
#####.#
Due to conservation of blizzard energy, as a blizzard reaches the wall of the valley, a new blizzard forms on the opposite side of the valley moving in the same direction. After another minute, the bottom downward-moving blizzard has been replaced with a new downward-moving blizzard at the top of the valley instead:
#.#####
#...v.#
#..>..#
#.....#
#.....#
#.....#
#####.#
Because blizzards are made of tiny snowflakes, they pass right through each other. After another minute, both blizzards temporarily occupy the same position, marked 2:
#.#####
#.....#
#...2.#
#.....#
#.....#
#.....#
#####.#
After another minute, the situation resolves itself, giving each blizzard back its personal space:
#.#####
#.....#
#....>#
#...v.#
#.....#
#.....#
#####.#
Finally, after yet another minute, the rightward-facing blizzard on the right is replaced with a new one on the left facing the same direction:
#.#####
#.....#
#>....#
#.....#
#...v.#
#.....#
#####.#
This process repeats at least as long as you are observing it, but probably forever.
Here is a more complex example:
#.######
#>>.<^<#
#.<..<<#
#>v.><>#
#<^v^^>#
######.#
Your expedition begins in the only non-wall position in the top row and needs to reach the only non-wall position in the bottom row. On each minute, you can move up, down, left, or right, or you can wait in place. You and the blizzards act simultaneously, and you cannot share a position with a blizzard.
In the above example, the fastest way to reach your goal requires 18 steps. Drawing the position of the expedition as E, one way to achieve this is:
Initial state:
#E######
#>>.<^<#
#.<..<<#
#>v.><>#
#<^v^^>#
######.#
Minute 1, move down:
#.######
#E>3.<.#
#<..<<.#
#>2.22.#
#>v..^<#
######.#
Minute 2, move down:
#.######
#.2>2..#
#E^22^<#
#.>2.^>#
#.>..<.#
######.#
...
Minute 17, move down:
#.######
#2.v.<>#
#<.<..<#
#.^>^22#
#.2..2E#
######.#
Minute 18, move down:
#.######
#>2.<.<#
#.2v^2<#
#>..>2>#
#<....>#
######E#
(SEE WEBSITE FOR FULL EXAMPLE)
What is the fewest number of minutes required to avoid the blizzards and reach the goal?
To begin, get your puzzle input.
--- Part Two ---
As the expedition reaches the far side of the valley, one of the Elves looks especially dismayed:
He forgot his snacks at the entrance to the valley!
Since you're so good at dodging blizzards, the Elves humbly request that you go back for his snacks. From the same initial conditions, how quickly can you make it from the start to the goal, then back to the start, then back to the goal?
In the above example, the first trip to the goal takes 18 minutes, the trip back to the start takes 23 minutes, and the trip back to the goal again takes 13 minutes, for a total time of 54 minutes.
What is the fewest number of minutes required to reach the goal, go back to the start, then reach the goal again?
Although it hasn't changed, you can still get your puzzle input.
Input
input = Kino.Input.textarea("Please paste your input file:")input = input |> Kino.Input.read()"#.####################################################################################################\n#>^v^v>><.>>><>^v<>^v>v<>^<<>>v>>.>><v>^<>^.<>v.>v^>vvvv<<<<>>^v^^^>><><.^^^.<<<>><^v^vv^v<.v.v>>.vv<#\n#>^><>^v^<>.<v><.<.v<v>vv<^<vvvv.^^...<<<^^vv<<v<>>>>v^<>>^^^><.>>>>v<<>^.>.^^<v<.><<.<><.>>>^^^>>.<>#\n#<.vvv^^v>^<<^^^>.^<..v.v<<^>vv<>>>v^>vv<><v<<vv<v^>v<^^^^v>.<.vv><v>v<v<^v^>>^<^^<>^>v^<^.^^v><>.><>#\n#>..<^^<>>v>><>vv^<v.^v.>^<.v^<v><<^<><v^v<.vv^>>vvv.vvv<>v>><<.>^><v^<<<v<<>><v><^v.v.<>^>v><v<^<<.>#\n#>^^<v>v><^<^>^<vvv^.>^^><^>><^^.vv>v<>v<>^>^v><v>>.>>^<v><^v^v^>v^<.<v^^^<>vvv^^<.<v<>>>.^>><<.vvv.>#\n#><v>v^>^<>v^>>^^<>.><^v<^vvv>vv<.><>v>v<..<^>>v^v<<<<v>v^.<<<^^^^.^v^<<>^vvv>^><.^v<^<>vv><<^<>^<^<<#\n#.^vvv<vv>^^v<>v<<v^^>.<<<v><<vv<v>>^<vv<v>><<^>^vv<<>^<<>^v.>>.<>>^<^<v<^^^<.vv^vv><^><v^^v>v^v>^vv.#\n#<v.>^<^><^..>^.>>v>>vv<^<.<vv<<v^v<.vvv>>.^v^^<^v<^<.^vv>v>^><v<v^>^v>>>>^^^v>^^>>>v<v^vv<.^><vv<>^<#\n#><>v^>^v<.<.>.<^.<>>^^>v^<v^<v>vvv<<^>vv<^^>^<^>v<.^.v<<.v.v^v>v><>..^^<.v^^<.<<<<<><>v><v<^^v<^<vv<#\n#><<>v><>^^^.<.<<>^v>v^>^>>>>v>.^>.v>.^>^.v<^<>v.v>v^v^^>^v>>>.<^v^^.>>>>^<<v<.^^>>>>^><v^v>vvv^>^><<#\n#><vvvv.>v^.v>>><>^>><><v^<.>.^<^v.>.^<^>>^v<.<^^v<^><..<vv^v<>vv<<vv^v.>>^.<v^>^>^<^<^>><><v<<>.><<>#\n#>.<^^v^><<<.v<vv<>^<>v^vv<^^.<>>.^<vv>>^.v.>^><v^^>.<<>v<>^v<v><v^^<v.v><<>vvv.v<>v>vvv^<>v^>^v<<<><#\n#.>><<vv><>vv>v..<<^^vv^>^<>^^v>v^vv>.><>^<vv^^<v><^^>><>>v<<v>^v^^><>.^.vv>v.^^>^vv<><.>>^^<^<><>v>.#\n#><<v>v<><^<<^><..<^>v<<^.^^<.^^v<>>^v>.^^^<<v>v>><><.<>>^v<^.v<vv<<^>>>vv^<vv.>^^^<><>v.>.^<^v<vv^><#\n#<.>vvv<v>^.vv.>.<v^.<..<>^v<>>^^vv>.>^v^>>>vv^<v><^v.v^>>>>><>v>v<>v^^>.^^v>^v><<>vv^<><>>v<^<v<<<<>#\n#<v<><^v<>>.<v^><<>^>v<<.v^v.<^v.^<vv<.v.^<v><><><v^^>v<>.vv^>vv<<^^<^^^><<>^>.^v<<<^<^<^^>>vv.<v.v<.#\n#<>vv^^<<^^^v^^<v^vvv^>^^.vvv^^^^v^>^^^v<^v><<^^^.<><v.vv<<^v<^>^><.^><^<>.v>^vv^v<<^<.<^.^>vv>^v>^<.#\n#<.vv>><.<vv<^^^<.^v><>>>><<^^<><^<vv<<>^v..>v<^^v><^><<^^^<<>^^>.>v><^<v<><v>v^<v<v^v.vv>v^<<<v>.^>>#\n#<^vv<<v^><>^^<<^.<v^>^vv.><^>v.>^vv.<^v^^<v<<v<><^<>v<<v<<><>^v^>v^^^><^>>^.<v.^<.^^.v<^v<>>.<<<v>^<#\n#>>..^^^<v.v<>>^^<v^..^vv<>.<>>>^><>^<v><<.v.^v^^<^<><>..>^<>.>^^<v.^v<v<<^v>^vv.v>.<.^^<v^<<>^^<^v<.#\n#>>vvv^v^v^>v<<vv.^.^<<vv^>^>v<.^>^<v^>^^<^<>^.><^v<<<v>>..v><>v^>^>><^^<>.v<vv^>>>>v<^v.v>v.>^vv^.^<#\n#<^<>.^<>>^<^v>.^v.><.<v.v.^v><^>.>^<>^^>>^^^.<^<>><>^><vvv^>^.v^^v>vv<<vvv>^.^>><.<>^.^<>.>>>v>v<v^>#\n#<^^vv<<^<^.<^>^<vv.>>.>><^<^^^<<>.v>v>v>v.^<<v<.<>v<<<>v<>^<v.^<<<v<<>>>>.^><^^<>>>^<><^.^.v^^v^^>..#\n#..v>vv^<vv>><^>^^^<v>><v^^><>.^^><^<><>^>><v>^v<><v.^<>><.>^>v^>^v<><v^v>><><^>v>.v^v>v<><.^^.>.v.^<#\n#.<v>v<^v.<<<vv<>^v^vv<^v^>^^v^<>^>>vv<^^v^^^^<.^v<>^<<^<v^v<><v>v^<<>>.vvv.>>^v>>>vv<<><^v<v^v<<.>>>#\n#<<vv.v^.>..v><v<><vv<<<<.>vv>v>>^v^v<v^<v<>v<<v^v^v^<<v^>v<^^^>v<^^^^^>>><<v<>v<>.>v^v<><.<<v<>^.^^.#\n#>>>>>^^.><^<>^<>v>.<^vv^^<>>^v><^<^>vv^<v><.>^v>.v<v<>>>>^.^>^v^^^<vvv^.<<..^v<.>^><<>><<^<.<<v<>^v<#\n#<.v.^>.^<.v<^^<.<^<<^.^<>><^<<^<><.<>.><<<><^v<v>^^v<<v>><^<>>^>^^>vv>^<.^<v><>.><v^v<vv^<^^<v>>>^v<#\n#<>v^>^^v>>^<^>v>>>.>^.><>..>^v>><>v<>^>.^v<<<<^>v>v><v^<^>^^>^<<>^>vv><<<v>v^^v<vv<^<^>vv^<.v^<^v>^>#\n#><<vvv.<<<vv<vv^^^v^v<^>vv^<>^^v<>v<^^^^><>^^>^<<<>v.vv^<><<><.^<<<^>>^vv<.v^^>vv><<<>v.<><v^><^^^v.#\n#<><v<v><^<^^vvv^>><><<<.<<vv<^<>.^<>>^v^>>vvv>>v..><<^^.v<><^^><^>>^<<v<<^v^>v>vvvvv...^<v^<^<v<.^<.#\n#>><<<v^^v^>^<<.>>vvv^v<^<>.^v^<^v<^^>>v<.>v<v..^^v.^>.v>^>>v^<<.v<^<..>.v<<..^^^v>v<.^<.>v^v^<v^v>^>#\n#<^>v<>^<<v>>vv>.><^v<^.><<^v>v<^<<<v^.^v.><>v><>^v><<<v.>vv<>vv>><>>^><><v>>v^.^v<<v^vvv<.<<>.v^^v<>#\n#<^<^><<>v..>v^>v>.v<<<^<<<v^v<<>^<.<.<v.v^<><v^<<>^><vv.v>>vv^.v^.^^>^^<<^^>.vv<.>.^^<>.<<v><vv<<>>>#\n#>v>>vv<.v<v.<^.^^><><^^v>^>>>>^>vv><<v>vv^.>>v^^vv^v^.>^v<>>>^^^>..vv^.^><..>>v<>^>^^<<.v<>v^^^v>^v>#\n####################################################################################################.#"
Solution
defmodule Day24 do
defdelegate parse(input), to: __MODULE__.Input
def part1(input) do
grid = parse(input)
grid
|> journey([grid.start_point], grid.end_point, 1)
|> elem(0)
end
def part2(input) do
grid = parse(input)
with {min_a, grid_a} <- journey(grid, [grid.start_point], grid.end_point, 1),
{min_b, grid_b} <- journey(grid_a, [grid.end_point], grid.start_point, 1),
{min_c, _grid_c} <- journey(grid_b, [grid.start_point], grid.end_point, 1) do
min_a + min_b + min_c
end
end
def journey(grid, points, destination, minute) do
with new_grid <- progress_blizzard(grid),
new_points <- expand_points(points, new_grid) do
if destination in new_points do
{minute, new_grid}
else
journey(new_grid, new_points, destination, minute + 1)
end
end
end
def expand_points(points, grid) do
points
|> Enum.flat_map(fn {x, y} ->
[
{x, y},
{x - 1, y},
{x + 1, y},
{x, y - 1},
{x, y + 1}
]
end)
|> Enum.uniq()
|> Enum.filter(fn
xy when xy in [grid.start_point, grid.end_point] ->
true
{x, y} when x in grid.min_x..grid.max_x and y in grid.min_y..grid.max_y ->
Enum.empty?(grid[{x, y}])
_ ->
false
end)
end
def progress_blizzard(grid) do
grid
|> Enum.reduce(grid, fn
{_, []}, acc ->
acc
{xy, directions}, acc when is_list(directions) ->
Enum.reduce(directions, acc, &move_direction(&1, xy, &2))
_, acc ->
acc
end)
end
def move_direction(direction, xy, grid) do
grid
|> Map.update!(
xy,
fn list -> List.delete(list, direction) end
)
|> Map.update!(
new_xy(direction, xy, grid),
fn list -> [direction | list] end
)
end
def new_xy(?^, {x, y}, %{min_y: y, max_y: max_y}), do: {x, max_y}
def new_xy(?v, {x, y}, %{max_y: y, min_y: min_y}), do: {x, min_y}
def new_xy(?<, {x, y}, %{min_x: x, max_x: max_x}), do: {max_x, y}
def new_xy(?>, {x, y}, %{max_x: x, min_x: min_x}), do: {min_x, y}
def new_xy(?^, {x, y}, _), do: {x, y - 1}
def new_xy(?v, {x, y}, _), do: {x, y + 1}
def new_xy(?<, {x, y}, _), do: {x - 1, y}
def new_xy(?>, {x, y}, _), do: {x + 1, y}
def draw(grid, points \\ []) do
0..(grid.max_y + 1)
|> Enum.each(fn y ->
0..(grid.max_x + 1)
|> Enum.map(fn x ->
cond do
{x, y} in points ->
"E"
grid.start_point == {x, y} ->
"."
grid.end_point == {x, y} ->
"."
x < grid.min_x ->
"#"
x > grid.max_x ->
"#"
y < grid.min_y ->
"#"
y > grid.max_y ->
"#"
grid[{x, y}] == [] ->
"."
true ->
case grid[{x, y}] do
[] -> "."
[dir] -> List.to_string([dir])
list -> list |> length() |> to_string()
end
end
end)
|> Enum.join("")
|> IO.puts()
end)
grid
end
defmodule Input do
def parse(input) when is_binary(input) do
input
|> String.split("\n", trim: true)
|> parse()
end
def parse(input) when is_list(input) do
input =
input
|> Enum.map(&String.to_charlist/1)
|> Enum.with_index()
first_row = Enum.at(input, 0)
last_row = Enum.at(input, -1)
rows = Enum.slice(input, 1..-2)
grid = %{
min_x: 1,
max_x: (first_row |> elem(0) |> length()) - 2,
min_y: 1,
max_y: (last_row |> elem(1)) - 1,
start_point: {
first_row |> elem(0) |> Enum.find_index(&(&1 == ?.)),
first_row |> elem(1)
},
end_point: {
last_row |> elem(0) |> Enum.find_index(&(&1 == ?.)),
last_row |> elem(1)
}
}
Enum.reduce(rows, grid, &parse_row/2)
end
def parse_row({chars, y}, grid) do
chars
|> Enum.with_index()
|> Enum.reduce(grid, fn
{?#, _}, acc -> acc
{?., x}, acc -> Map.put(acc, {x, y}, [])
{char, x}, acc -> Map.put(acc, {x, y}, [char])
end)
end
end
end{:module, Day24, <<70, 79, 82, 49, 0, 0, 39, ...>>,
{:module, Day24.Input, <<70, 79, 82, ...>>, {:parse_row, 2}}}
What is the fewest number of minutes required to avoid the blizzards and reach the goal?
Your puzzle answer was 260.
Day24.part1(input)260
What is the fewest number of minutes required to reach the goal, go back to the start, then reach the goal again?
Your puzzle answer was 747.
Day24.part2(input)747
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 Day24Test do
use ExUnit.Case, async: false
setup_all do
[
input: "#.######\n#>>.<^<#\n#.<..<<#\n#>v.><>#\n#<^v^^>#\n######.#"
]
end
describe "part1" do
test "returns expected value", %{input: input} do
assert Day24.part1(input) == 18
end
end
describe "part2" do
test "returns expected value", %{input: input} do
assert Day24.part2(input) == 54
end
end
end
ExUnit.run()..
Finished in 0.00 seconds (0.00s async, 0.00s sync)
2 tests, 0 failures
Randomized with seed 427176
%{excluded: 0, failures: 0, skipped: 0, total: 2}
Benchmarking
# https://github.com/bencheeorg/benchee
Benchee.run(
%{
"Part 1" => fn -> Day24.part1(input) end,
"Part 2" => fn -> Day24.part2(input) end
},
memory_time: 2,
reduction_time: 2
)
nilOperating System: macOS
CPU Information: Apple M1
Number of Available Cores: 8
Available memory: 8 GB
Elixir 1.14.2
Erlang 25.1.2
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 1.32 0.76 s ±1.82% 0.76 s 0.78 s
Part 2 0.50 2.01 s ±0.14% 2.01 s 2.01 s
Comparison:
Part 1 1.32
Part 2 0.50 - 2.64x slower +1.25 s
Memory usage statistics:
Name average deviation median 99th %
Part 1 0.93 GB ±0.02% 0.93 GB 0.93 GB
Part 2 2.65 GB ±0.00% 2.65 GB 2.65 GB
Comparison:
Part 1 0.93 GB
Part 2 2.65 GB - 2.84x memory usage +1.72 GB
Reduction count statistics:
Name average deviation median 99th %
Part 1 31.35 M ±0.00% 31.35 M 31.35 M
Part 2 86.68 M ±0.00% 86.68 M 86.68 M
Comparison:
Part 1 31.35 M
Part 2 86.68 M - 2.77x reduction count +55.33 M
nil
