18 lines
684 B
Haskell
18 lines
684 B
Haskell
import qualified Data.Map.Strict as M
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blinkStone :: (Int, Int) -> [(Int, Int)]
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blinkStone (0, n) = [(1, n)]
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blinkStone (s, n) = let ss = show s
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nDigit = length ss
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in if even nDigit
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then zip (map read [take (nDigit `div` 2) ss, drop (nDigit `div` 2) ss]) [n, n]
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else [(s * 2024, n)]
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blink :: Int -> M.Map Int Int -> M.Map Int Int
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blink 0 m = m
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blink n m = blink (n - 1) $ M.fromListWith (+) $ concatMap blinkStone $ M.toList m
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main = do
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contents <- M.fromListWith (+) . flip zip (repeat 1) . map read . words <$> readFile "day11.txt"
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print . M.foldl (+) 0 $ blink 25 contents
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