51 lines
1.4 KiB
Haskell
51 lines
1.4 KiB
Haskell
module Main where
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import qualified AoC as A (extract)
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import Data.Bool (bool)
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import Data.List (sortBy, tails)
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import qualified Data.Set as S
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import Text.Parsec (char, digit, many1, newline, parse, sepBy1, sepEndBy1)
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import Text.Parsec.String (Parser)
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type Rule = (Int, Int)
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type Rules = S.Set Rule
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type Update = [Int]
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parseRules :: Parser (Rules, [Update])
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parseRules = do
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rules <- S.fromList <$> parseRule `sepEndBy1` newline
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newline
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updates <- parseUpdate `sepEndBy1` newline
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return (rules, updates)
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where
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parseRule :: Parser Rule
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parseRule = (,) <$> (read <$> many1 digit <* char '|') <*> (read <$> many1 digit)
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parseUpdate :: Parser Update
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parseUpdate = (read <$> many1 digit) `sepBy1` char ','
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middle :: [a] -> a
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middle xs = xs !! (length xs `div` 2)
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isOrdered :: Rules -> Update -> Bool
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isOrdered rules (first : rest) = all (flip S.member rules . (,) first) rest
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isOrdered _ _ = False
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part1 :: Rules -> [Update] -> Int
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part1 rules = sum . map middle . filter (all (isOrdered rules) . init . tails)
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part2 :: Rules -> [Update] -> Int
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part2 rules =
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sum
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. map (middle . sortBy (\x -> bool GT LT . flip S.member rules . (,) x))
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. filter (not . all (isOrdered rules) . init . tails)
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main :: IO ()
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main =
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do
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raw <- readFile "./inputs/day5.in"
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let (rules, updates) = A.extract $ parse parseRules "" raw
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putStr "Part 1: " >> print (part1 rules updates)
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putStr "Part 2: " >> print (part2 rules updates)
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