82 lines
3.1 KiB
Haskell
82 lines
3.1 KiB
Haskell
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-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Applicative.Permutations
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import Control.Monad (void, when)
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import qualified Data.Char as C
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import Data.Either
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import Data.Functor
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import qualified Data.Heap as H
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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.Ratio
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import qualified Data.Set as S
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import qualified Data.Vector as V
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import qualified Data.Vector.Unboxed as VU
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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 = 2
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type Hail = (Rational, Rational, Rational, Rational, Rational, Rational)
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type Input = [Hail]
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type Parser = Parsec Void String
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parseNumber :: Parser Integer
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parseNumber = read <$> some (char '-' <|> digitChar) <* optional (char ',') <* optional hspace <* optional (char '@' <* hspace)
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parseHail :: Parser Hail
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parseHail = (,,,,,) <$> (fromInteger <$> parseNumber)
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<*> (fromInteger <$> parseNumber)
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<*> (fromInteger <$> parseNumber)
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<*> (fromInteger <$> parseNumber)
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<*> (fromInteger <$> parseNumber)
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<*> (fromInteger <$> parseNumber)
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parseInput' :: Parser Input
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parseInput' = some (parseHail <* 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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compute :: Rational -> Rational -> Input -> Int
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compute mini maxi = compute'
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where
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compute' :: Input -> Int
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compute' (_:[]) = 0
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compute' ((x1, y1, _, a1, b1, _):hs) = L.foldl' computeOne 0 hs + compute' hs
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where
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(x2, y2) = (x1 + a1, y1 + b1)
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computeOne :: Int -> Hail -> Int
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computeOne acc (x3, y3, _, a3, b3, _) | valid = acc + 1
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| otherwise = acc
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where
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valid | denominator == 0 || t < 0 || u < 0 = False
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| x >= mini && x <= maxi && y >= mini && y <= maxi = True
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| otherwise = False
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(x4, y4) = (x3 + a3, y3 + b3)
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denominator = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4)
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a = x1 * y2 - y1 * x2
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b = x3 * y4 - y3 * x4
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numeratorX = b * a1 - a * a3
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numeratorY = b * b1 - a * b3
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(x, y) = (numeratorX / denominator, numeratorY / denominator)
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(t, u) = ((x - x1) / a1, (x - x3) / a3)
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main :: IO ()
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main = do
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example <- parseInput "example"
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let exampleOutput = compute 7 27 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 200000000000000 400000000000000 input
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