diff --git a/2020/day17/day17.hs b/2020/day17/day17.hs
index 8d86141..c20b113 100644
--- a/2020/day17/day17.hs
+++ b/2020/day17/day17.hs
@@ -1,51 +1,40 @@
-{-# LANGUAGE ParallelListComp #-}
-import Linear.V3
-import Linear.V4
+import Control.Lens
 import Control.Monad
 import Data.List
-import Control.Lens
-import Data.Function
+import Linear.V2
+import Linear.V3
+import Linear.V4
+import Linear.Vector
 
 main :: IO ()
 main = do
-    input <- lines <$> readFile "input"
-    print input
---    print $ toV3 input
---    print $ updateNeighbours $ toV3 input
-    let final =  flip (!!) 6 $ iterate step $ toV3 input
-    putStrLn $ visualize (-2) final
-    putStrLn $ visualize (-1) final
-    putStrLn $ visualize 0 final
-    print $ length final
+  input <- lines <$> readFile "input"
+  let a = toVec input
+      _ = a :: [V4 Int]
+  print $ day17 a
 
-visualize :: Int -> [V3 Int] -> String
-visualize z vs = unlines $ visualize' (filter ((==z) . (^._z)) vs) (replicate height (replicate width '.'))
-    where x' = maximumBy (compare `on` (^._x)) vs
-          y' = maximumBy (compare `on` (^._y)) vs
-          x = minimumBy (compare `on` (^._x)) vs
-          y = minimumBy (compare `on` (^._y)) vs
-          width = (x'-x) ^._x +1
-          height = (y'-y) ^._y +1
-          visualize' [] arr = arr
-          visualize' ((V3 x'' y'' _):vs_f) arr = visualize' vs_f (beg++newLine:end)
-              where (beg,line:end) = splitAt (y''-(y^._y)) arr
-                    (beg',_:end') = splitAt (x''-(x^._x)) line
-                    newLine = beg' ++ '#' : end'
+day17 = length . flip (!!) 6 . iterate step
 
+toVec input =
+  [ zero & _xy .~ V2 x y
+  | (y, line) <- zip [0 ..] input
+  , (x, c) <- zip [0 ..] line
+  , c == '#'
+  ]
 
+step state =
+  (nub .
+   concatMap fst .
+   filter f . ap zip (map length) . group . sort . updateNeighbours)
+    state
+  where
+    f (x, n) = n == 3 || n == 2 && head x `elem` state
 
-toV3 :: [String] -> [V3 Int]
-toV3 input = [V3 x y 0 | (y,line)<-zip [0..] input, (x,c)<-zip [0..] line, c=='#']
-
-step :: [V3 Int] -> [V3 Int]
-step state = (nub . concatMap fst . filter f . ap zip (map length) . group . sort . updateNeighbours) state
-    where f (x,n) = n==3 || n==2 && head x `elem` state
-
-updateNeighbours :: [V3 Int] -> [V3 Int]
-updateNeighbours = concatMap f where
-    f coord = [coord + V3 x y z | [x,y,z]<-replicateM 3 [(-1)..1] \\ [[0,0,0]]]
-
-mapI :: Num b => (a -> b -> c) -> [a] -> [c]
-mapI f l = mapI' f 0 l where
-    mapI' _ _ []     = []
-    mapI' f n (x:xs) = f x n : mapI' f (n+1) xs
+updateNeighbours = concatMap f
+  where
+    f coord =
+      [ coord + v
+      | v <-
+          filter (/= zero) $
+          nub $ map sum $ subsequences (ap (++) (map negate) basis)
+      ]