95 lines
3.1 KiB
Haskell
95 lines
3.1 KiB
Haskell
{-# LANGUAGE NamedFieldPuns #-}
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module Day16 where
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import AoC
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import Data.List
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import Data.Maybe
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import qualified Data.Set as S
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import Data.Set (Set)
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import Text.ParserCombinators.ReadP
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import Text.Read.Lex
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data Field = Field { name :: String
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, valids :: Set Int
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} deriving (Show)
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type Ticket = [Int]
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data Input = Input { fields :: [Field]
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, myTicket :: Ticket
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, otherTickets :: [Ticket]
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} deriving (Show)
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line :: ReadP a -> ReadP a
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line p = p <* char '\n'
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parseField :: ReadP Field
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parseField = do
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name <- many1 $ satisfy (/=':')
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string ": "
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ranges <- parseRange `sepBy` string " or "
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let valids = S.fromList . concat . map (uncurry enumFromTo) $ ranges
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return $ Field { name, valids }
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where parseRange = do
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n1 <- readDecP
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char '-'
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n2 <- readDecP
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return (n1, n2)
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parseTicket :: ReadP Ticket
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parseTicket = readDecP `sepBy` char ','
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parseInput :: ReadP Input
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parseInput = do
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fields <- many1 $ line parseField
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line $ string ""
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line $ string "your ticket:"
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myTicket <- line parseTicket
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line $ string ""
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line $ string "nearby tickets:"
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otherTickets <- many1 $ line parseTicket
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return $ Input {fields, myTicket, otherTickets }
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matchesAnyField :: [Field] -> Int -> Bool
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matchesAnyField fields n = any (n `S.member`) . map valids $ fields
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iterateUntilNothing :: (a -> Maybe a) -> a -> a
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iterateUntilNothing f x = maybe x (iterateUntilNothing f) $ f x
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data Resolve a = Resolved a | Choice (Set a) deriving (Show)
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resolve :: Ord a => [[a]] -> Maybe [a]
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resolve = sequence . map fromResolved . iterateUntilNothing resolve' . map (Choice . S.fromList)
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where fromResolved (Resolved x) = Just x
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fromResolved _ = Nothing
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findSingletonChoice :: [Resolve a] -> Maybe (a, [Resolve a])
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findSingletonChoice [] = Nothing
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findSingletonChoice (x:xs) =
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case x of
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Choice s | S.size s == 1 -> let [r] = S.elems s
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in Just (r, Resolved r : xs)
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_ -> fmap (\(r, rest) -> (r, x:rest)) $ findSingletonChoice xs
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resolve' :: Ord a => [Resolve a] -> Maybe [Resolve a]
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resolve' xs = do
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(x, xs') <- findSingletonChoice xs
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return $ map (dropChoice x) xs'
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where dropChoice x (Choice s) = Choice (S.delete x s)
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dropChoice _ r = r
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part1 :: Input -> Int
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part1 Input { fields, otherTickets } = sum . filter (not . matchesAnyField fields) . concat $ otherTickets
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part2 :: Input -> Int
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part2 Input { fields, myTicket, otherTickets } = product departureValues
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where validTickets = filter (all $ matchesAnyField fields) otherTickets
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columns = transpose validTickets
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fieldNames = fromJust . resolve . map findPossibleFields $ columns
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departureIndices = findIndices ("departure" `isPrefixOf`) fieldNames
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departureValues = map (myTicket !!) departureIndices
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findPossibleFields col = map name . filter (\field -> all (`S.member` valids field) col) $ fields
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main = runAoC (fromJust . oneCompleteResult parseInput) part1 part2
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