38 lines
1.1 KiB
Haskell
38 lines
1.1 KiB
Haskell
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import Aoc
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parseLine :: String -> [Bool]
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parseLine = map toBool
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where
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toBool '.' = False
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toBool '#' = True
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countNeighbours :: [[Bool]] -> (Bool, Int)
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countNeighbours [[a, b, c], [d, e, f], [g, h, i]] = (e, length (filter id [a, b, c, d, f, g, h, i]))
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survives :: (Bool, Int) -> Bool
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survives (False, n) = n == 3
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survives (True, n) = n == 2 || n == 3
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simulate :: [[Bool]] -> [[Bool]]
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simulate = kernelMap (survives . countNeighbours) (Just False)
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numOn :: [[Bool]] -> Int
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numOn = sum . map (sum . map fromEnum)
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doSimulate :: ([[Bool]] -> [[Bool]]) -> [[Bool]] -> Int
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doSimulate simulate board = numOn $ iterate simulate board !! 100
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part1 :: [[Bool]] -> Int
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part1 = doSimulate simulate
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part2 :: [[Bool]] -> Int
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part2 = doSimulate simulate' . keepOn
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where
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updateFirst f (x:xs) = f x: xs
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updateLast f (x:xs) = if null xs then [f x] else x: updateLast f xs
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updateEnds f = updateFirst f . updateLast f
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keepOn = updateEnds (updateEnds $ const True)
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simulate' = keepOn . simulate
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main :: IO ()
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main = aocMain (map parseLine) part1 part2
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