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module Main where
import Data.List (sortOn)
import Data.Map (Map, (!))
import qualified Data.Map as Map
import Data.Maybe
import Utils
dirs = [ (-1,-1), (0,-1), (1,-1)
, (-1, 0), (1, 0)
, (-1, 1), (0, 1), (1, 1)
]
adjs1 m pt = howMany (== '#') $ mapMaybe ((`Map.lookup` m) . add pt) dirs
inGrid (x, y) w h = x < w && x >= 0 && y < h && y >= 0
adjs2 grid pt w h = howMany ((== '#') . head)
$ filter (not . null)
$ map (dropWhile (== '.')
. map (grid !)
. takeWhile (inside (0, 0) (w-1, h-1))
. map ($ pt)
. repeatF
. add)
dirs
rule1 w h m pt@(x, y) = if as == 0 then '#' else 'L'
where as = adjs2 m pt w h
rule2 w h m pt@(x, y) = if as >= 5 then 'L' else '#'
where as = adjs2 m pt w h
doStep w h m = Map.mapWithKey fn m
where fn k 'L' = rule1 w h m k
fn k '#' = rule2 w h m k
fn k '.' = '.'
stepWhile prev w h
| prev == next = next
| otherwise = stepWhile next w h
where next = doStep w h prev
main :: IO ()
main = do
n <- readFile "input/11"
let (grid, width, height) = makeGrid n
let solve1 = stepWhile grid width height
print $ howMany ((== '#') . snd) $ Map.toList solve1
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