75 lines
2.9 KiB
Haskell
75 lines
2.9 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Monad (void, when)
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import Data.Bits
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import Data.Functor
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import qualified Data.List as L
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import qualified Data.Map as M
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import Data.Maybe
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import Data.Ord (comparing)
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import qualified Data.Set as S
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import Data.Void (Void)
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import Text.Megaparsec
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import Text.Megaparsec.Char
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import Debug.Trace
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exampleExpectedOutput = 23
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type Input = [Int]
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type Parser = Parsec Void String
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parseInput' :: Parser Input
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parseInput' = some (read <$> some digitChar <* eol) <* eof
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> error $ errorBundlePretty bundle
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Right input' -> return input'
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type Seq = (Int, Int, Int, Int)
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type PriceMap = M.Map Seq Int
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compute :: Input -> Int
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compute input = trace (show bestSequence) maxBananas
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where
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(bestSequence, maxBananas) = S.foldl (\(s, n) s' -> let n' = fromJust $ M.lookup s' bananas
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in if n >= n' then (s, n)
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else (s', n')
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) ((0, 0, 0, 0), 0) allSeqs
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bananas :: PriceMap
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bananas = S.foldl (\acc s -> M.insert s (sum $ catMaybes $ map (M.lookup s) allPriceMaps) acc) M.empty allSeqs
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allSeqs :: S.Set Seq
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allSeqs = L.foldl' (\acc p -> S.union acc $ S.fromList $ M.keys p) S.empty allPriceMaps
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allPriceMaps :: [PriceMap]
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allPriceMaps = map (seqPrices M.empty) allPrices
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seqPrices :: PriceMap -> [Int] -> PriceMap
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seqPrices m s@(a:b:c:d:e:_) = seqPrices (let seq = (b-a, c-b, d-c, e-d) in case M.lookup seq m of
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Just _ -> m
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Nothing -> M.insert seq e m
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) (tail s)
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seqPrices m _ = m
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allPrices = map prices input
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prices :: Int -> [Int]
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prices s = fst $ L.foldl' next ([s `mod` 10], s) [1..2000]
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next :: ([Int], Int) -> Int -> ([Int], Int)
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next (acc, s) _ = let s' = prune $ mix (shift s 6) s
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s'' = prune $ mix (shift s' (-5)) s'
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s''' = prune $ mix (shift s'' 11) s''
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in (acc ++ [s''' `mod` 10], s''')
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mix :: Int -> Int -> Int
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mix = xor
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prune :: Int -> Int
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prune n = n `mod` 16777216
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main :: IO ()
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main = do
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example <- parseInput "example2"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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