31 lines
1,015 B
Haskell
31 lines
1,015 B
Haskell
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import AoC
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import Control.Monad
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import Data.List
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import Data.Maybe
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slidingWindow :: Int -> [a] -> [[a]]
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slidingWindow n xs
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| length xs < n = []
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| otherwise = take n xs : slidingWindow n (tail xs)
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summingTo :: (Eq a, Num a) => Int -> a -> [a] -> Maybe [a]
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n `summingTo` x = find ((==x) . sum) . replicateM n
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sublistSummingTo :: (Num a, Ord a) => a -> [a] -> Maybe [a]
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sublistSummingTo n = fmap snd . find ((== n) . fst) . scanl go (0, [])
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where go = dropNeeded .: addToAcc
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addToAcc (sum, parts) x = (sum+x, parts++[x])
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dropNeeded = fromJust . find ((<= n) . fst) . iterate dropPart
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dropPart (sum, (x:xs)) = (sum-x, xs)
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part1 :: [Int] -> Int
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part1 = snd . fromJust . find (not . uncurry doesSum) . map (\xs -> (init xs, last xs)) . slidingWindow 26
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where doesSum xs y = isJust $ 2 `summingTo` y $ xs
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part2 :: [Int] -> Int
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part2 xs = minimum range + maximum range
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where range = fromJust $ sublistSummingTo (part1 xs) xs
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main = runAoC (map read . lines) part1 part2
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