AdventOfCode/2020/day17/day17part2.exs

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Elixir
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2020-12-20 18:54:04 +00:00
defmodule Day17Part2 do
def run do
File.read!("input")
|> String.split("\n", trim: true)
|> parse_input()
|> boot(6)
|> Enum.count()
|> IO.puts()
end
def parse_input(input) do
{_y, cubes} =
Enum.reduce(input, {0, MapSet.new()}, fn row, {y, cubes} ->
{_x, cubes} =
Enum.reduce(String.graphemes(row), {0, cubes}, fn
".", {x, cubes} -> {x + 1, cubes}
"#", {x, cubes} -> {x + 1, MapSet.put(cubes, {x, y, 0, 0})}
end)
{y + 1, cubes}
end)
cubes
end
def boot(cubes, 0), do: cubes
def boot(cubes, count), do: boot(cycle(cubes), count - 1)
def cycle(cubes) do
{next_cubes, inactives} =
Enum.reduce(cubes, {MapSet.new(), MapSet.new()}, fn cube, {next_cubes, inactives} ->
{active_count, inactives} =
Enum.reduce(neighbours(cube), {0, inactives}, fn neighbour, {active_count, inactives} ->
if MapSet.member?(cubes, neighbour) do
{active_count + 1, inactives}
else
{active_count, MapSet.put(inactives, neighbour)}
end
end)
next_cubes = if active_count in 2..3, do: MapSet.put(next_cubes, cube), else: next_cubes
{next_cubes, inactives}
end)
Enum.reduce(inactives, next_cubes, fn inactive, next_cubes ->
active_neighbours =
inactive |> neighbours() |> MapSet.new() |> MapSet.intersection(cubes) |> Enum.count()
if active_neighbours == 3, do: MapSet.put(next_cubes, inactive), else: next_cubes
end)
end
def neighbours({x, y, z, w} = me) do
all =
for x <- (x - 1)..(x + 1),
y <- (y - 1)..(y + 1),
z <- (z - 1)..(z + 1),
w <- (w - 1)..(w + 1),
do: {x, y, z, w}
all -- [me]
end
end
Day17Part2.run()