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|
onLights =
File.stream!("inputs/day18.txt")
|> Enum.with_index()
|> Enum.flat_map(fn {line, y} ->
String.trim(line)
|> String.graphemes()
|> Enum.with_index()
|> Enum.filter(fn {on, _x} -> on == "#" end)
|> Enum.map(fn {_, x} -> {x, y} end)
end)
|> MapSet.new()
lightStream = fn initial, stuckLights ->
Stream.iterate(initial, fn onLights ->
newOnLights =
stuckLights ++
Enum.flat_map(0..99, fn y ->
Enum.filter(0..99, fn x ->
currentlyOn = MapSet.member?(onLights, {x, y})
neighborCount =
Enum.filter(
[
MapSet.member?(onLights, {x - 1, y - 1}),
MapSet.member?(onLights, {x, y - 1}),
MapSet.member?(onLights, {x + 1, y - 1}),
MapSet.member?(onLights, {x - 1, y}),
MapSet.member?(onLights, {x + 1, y}),
MapSet.member?(onLights, {x - 1, y + 1}),
MapSet.member?(onLights, {x, y + 1}),
MapSet.member?(onLights, {x + 1, y + 1})
],
& &1
)
|> Enum.count()
neighborCount == 3 || (currentlyOn && neighborCount == 2)
end)
|> Enum.map(fn x -> {x, y} end)
end)
MapSet.new(newOnLights)
end)
end
[after100] = Stream.drop(lightStream.(onLights, []), 100) |> Enum.take(1)
IO.puts("Lights on: #{MapSet.size(after100)}")
[after100Stuck] =
Stream.drop(lightStream.(onLights, [{0, 0}, {99, 0}, {0, 99}, {99, 99}]), 100) |> Enum.take(1)
IO.puts("Lights on with the corners stuck: #{MapSet.size(after100Stuck)}")
|
