Day 17: Solution

2020/day17/day17.hs

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+{-# LANGUAGE ParallelListComp #-}
+import Linear.V3
+import Linear.V4
+import Control.Monad
+import Data.List
+import Control.Lens
+import Data.Function
+
+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
+
+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'
+
+
+
+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

2020/day17/input

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+.#.####.
+.#...##.
+..###.##
+#..#.#.#
+#..#....
+#.####..
+##.##..#
+#.#.#..#

2020/day17/testinput

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+.#.
+..#
+###