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-- very slow with runghc, use ghc -O3 -o first first.hs
-- 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
exampleExpectedOutput = 4361
data Number = Number Int Int Int Int deriving Show -- Value x1 x2 y1
data Symbol = Symbol Int Int deriving (Eq, Ord, Show) -- x y
data Input = Input [Number] [Symbol] deriving Show
type Parser = Parsec Void String
parseNumber :: Parser Number
parseNumber = do
(SourcePos _ y' x1') <- getSourcePos
value <- read <$> some digitChar
(SourcePos _ _ x2') <- getSourcePos
let (x1, x2, y) = (unPos x1', unPos x2' - 1, unPos y')
return $ Number value x1 x2 y
parseSymbol :: Parser Symbol
parseSymbol = do
(SourcePos _ y' x') <- getSourcePos
void asciiChar
let (x, y) = (unPos x', unPos y')
return $ Symbol x y
parseNumbersAndSymbols :: Parser (Either Number Symbol)
parseNumbersAndSymbols = do
many $ void (char '.') <|> void eol
something <- (Left <$> parseNumber) <|> (Right <$> parseSymbol)
many $ void (char '.') <|> void eol
return something
parseInput' :: Parser Input
parseInput' = do
things <- some parseNumbersAndSymbols <* eof
return $ Input (lefts things) (rights things)
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 :: Input -> Int
compute (Input nums syms) = sum . map (\(Number v _ _ _) -> v) $ L.filter process nums
where
process :: Number -> Bool
process (Number _ x1 x2 y) = not . S.null $ S.fromList [Symbol x y|x<-[x1-1..x2+1],y<-[y-1..y+1]] `S.intersection` S.fromList syms
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
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