19 lines
695 B
Haskell
19 lines
695 B
Haskell
import Data.List (sort, inits, tails)
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import System.IO
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isSafe :: [Int] -> Bool
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isSafe xs = (isAscending xs || isDescending xs) && maximum distances <= 3 && minimum distances >= 1
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where isAscending xs = xs == sort xs
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isDescending xs = xs == reverse (sort xs)
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distances = map abs $ zipWith (-) xs (tail xs)
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removeLevel :: [Int] -> [[Int]]
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removeLevel xs = zipWith (++) ys zs
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where ys = map init $ tail (inits xs)
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zs = map tail $ init (tails xs)
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main = do
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contents <- lines <$> readFile "day2.txt"
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let reports = map read . words <$> contents
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print . length . filter (any isSafe) $ map removeLevel reports
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