54 lines
1.9 KiB
Haskell
54 lines
1.9 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators heap vector
|
|
module Main (main) where
|
|
|
|
import Control.Monad (void, when)
|
|
import qualified Data.List as L
|
|
import Data.Void (Void)
|
|
import Text.Megaparsec
|
|
import Text.Megaparsec.Char
|
|
|
|
type Pair = (Int, Int)
|
|
type Robot = (Pair, Pair)
|
|
type Input = [Robot]
|
|
|
|
type Parser = Parsec Void String
|
|
|
|
parseNumber :: Parser Int
|
|
parseNumber = read <$> some (digitChar <|> char '-')
|
|
|
|
parsePair :: Parser Pair
|
|
parsePair = (,) <$> parseNumber <* char ','
|
|
<*> parseNumber
|
|
|
|
parseRobot :: Parser Robot
|
|
parseRobot = (,) <$> (string "p=" *> parsePair)
|
|
<*> (string " v=" *> parsePair)
|
|
|
|
parseInput' :: Parser Input
|
|
parseInput' = some (parseRobot <* 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'
|
|
|
|
compute :: Int -> Int -> Input -> Int -- the minimum safety score is the answer
|
|
compute width height input = fst $ L.foldl' (\acc@(_, a) n@(_, b) -> if a > b then n else acc) (0, 1000000000) safeties
|
|
where
|
|
safeties = [(i, safety i)|i<-[0..width*height]]
|
|
mx = width `div` 2
|
|
my = height `div` 2
|
|
safety i = product $ L.foldl' score [0, 0, 0, 0] $ map (step i) input
|
|
step i ((x, y), (v, w)) = (((x + v * i) `mod` width), ((y + w * i) `mod` height))
|
|
score acc@[a, b, c, d] (x, y) | x < mx && y < my = [a+1, b, c, d]
|
|
| x > mx && y < my = [a, b+1, c, d]
|
|
| x < mx && y > my = [a, b, c+1, d]
|
|
| x > mx && y > my = [a, b, c, d+1]
|
|
| otherwise = acc
|
|
|
|
main :: IO ()
|
|
main = do
|
|
input <- parseInput "input"
|
|
print $ compute 101 103 input
|