55 lines
1.7 KiB
Haskell
55 lines
1.7 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators
|
|
module Main (main) where
|
|
|
|
import Control.Applicative.Permutations
|
|
import Control.Monad (void, when)
|
|
import Data.Char qualified as C
|
|
import Data.Either
|
|
import Data.List qualified as L
|
|
import Data.Map qualified as M
|
|
import Data.Maybe
|
|
import Data.Set qualified as S
|
|
import Data.Void (Void)
|
|
import Text.Megaparsec
|
|
import Text.Megaparsec.Char
|
|
|
|
import Debug.Trace
|
|
|
|
exampleExpectedOutput = 288
|
|
|
|
data Input = Input [Int] [Int] deriving Show -- time distance
|
|
|
|
type Parser = Parsec Void String
|
|
|
|
parseNumber :: Parser Int
|
|
parseNumber = read <$> some digitChar <* many (char ' ')
|
|
|
|
parseInput' :: Parser Input
|
|
parseInput' = Input <$> (string "Time:" *> many (char ' ') *> some parseNumber <* eol)
|
|
<*> (string "Distance:" *> many (char ' ') *> some parseNumber <* eol <* eof)
|
|
|
|
parseInput :: String -> IO Input
|
|
parseInput filename = do
|
|
input <- readFile filename
|
|
case runParser parseInput' filename input of
|
|
Left bundle -> error $ errorBundlePretty bundle
|
|
Right input' -> return input'
|
|
|
|
race :: Int -> Int -> Int
|
|
race limit record = limit + 1 - 2 * threshold
|
|
where
|
|
threshold = minTimeToBeat 0
|
|
minTimeToBeat :: Int -> Int
|
|
minTimeToBeat t | (limit - t) * t > record = t
|
|
| otherwise = minTimeToBeat (t+1)
|
|
|
|
compute :: Input -> Int
|
|
compute (Input times distances) = product $ zipWith race times distances
|
|
|
|
main :: IO ()
|
|
main = do
|
|
example <- parseInput "example"
|
|
let exampleOutput = compute example
|
|
when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
|
|
input <- parseInput "input"
|
|
print $ compute input
|