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diff --git a/2021/day20/20.hs b/2021/day20/20.hs
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+module Main where
+
+import Data.List (foldl', intercalate)
+import Data.Maybe (fromMaybe)
+
+type Picture = ([[Bool]], Bool) -- Visible region, colour of all pixels not visible
+
+readInteger :: [Bool] -> Int
+readInteger = foldl' (\acc x -> acc * 2 + boolToDigit x) 0
+  where boolToDigit True = 1
+        boolToDigit False = 0
+
+parseLine :: String -> [Bool]
+parseLine = map charToBool
+  where charToBool '#' = True
+        charToBool '.' = False
+
+(!?) :: [a] -> Int -> Maybe a
+xs !? n | n < 0 || n >= (length xs) = Nothing
+        | otherwise                 = Just (xs!!n)
+
+getPixel :: Picture -> Int -> Int -> Bool
+getPixel (p, d) x y = fromMaybe d $ (p !? y) >>= (!? x)
+
+getNeighbours :: Picture -> Int -> Int -> [Bool]
+getNeighbours p x y = [getPixel p (x + dx) (y + dy) | dy <- [(-1)..1], dx <- [(-1)..1]]
+
+getNewPixel :: Picture -> [Bool] -> Int -> Int -> Bool
+getNewPixel p alg x y = alg !! (readInteger $ getNeighbours p x y)
+
+printPic :: Picture -> String
+printPic = (intercalate "\n") . (map printLine) . fst 
+  where printLine = map printBool
+        printBool True = '#'
+        printBool False = '.'
+
+newDefault :: Bool -> [Bool] -> Bool
+newDefault True alg = alg!!511
+newDefault False alg = alg!!0
+
+applyAlgorithm :: Picture -> [Bool] -> Picture
+applyAlgorithm pic@(vis, def) alg = ([[getNewPixel pic alg x y | x <- [(-1)..mx]] | y <- [(-1)..my]], newDefault def alg)
+  where mx = length (vis!!0) + 1
+        my = length vis + 1
+
+parseFile :: String -> ([Bool], Picture)
+parseFile s = (parseLine alg, (map parseLine ls, False))
+  where (alg:_:ls) = lines s
+
+countPixels :: Picture -> Int
+countPixels = foldr (+) 0 . map (length . filter id) . fst
+
+main :: IO ()
+main = do
+  input <- readFile "./input"
+  let (alg, pic) = parseFile input
+  let pic2 = foldr (\_ p -> applyAlgorithm p alg) pic [1..2]
+  putStrLn $ "Part 1: " ++ (show $ countPixels pic2)
+
+  let pic50 = foldr (\_ p -> applyAlgorithm p alg) pic [1..50]
+  putStrLn $ "Part 2: " ++ (show $ countPixels pic50)