18 lines
567 B
Haskell
18 lines
567 B
Haskell
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import AoC
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import Data.List
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pairs :: [a] -> [(a, a)]
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pairs xs = zipWith (,) xs (tail xs)
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part1 :: [Int] -> Int
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part1 = product . map length . group . sort . map (uncurry $ flip (-)) . pairs
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numArrangements :: [Int] -> Int
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numArrangements = snd . head . go
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where go xs = foldr (\x acc -> (x, sum . map snd . takeWhile (\(y, _) -> x-y <= 3) $ acc) : acc) [(last xs, 1)] $ init xs
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main = runAoC (addPhonePort . sortReverse . (0:) . map read . lines) part1 numArrangements
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where addPhonePort (x:xs) = (x+3):x:xs
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sortReverse = sortBy (flip compare)
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