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author | Julien Dessaux | 2024-12-08 16:10:32 +0100 |
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committer | Julien Dessaux | 2024-12-08 16:10:32 +0100 |
commit | 3e098a4eed96c031d335644e4b30608058ebb000 (patch) | |
tree | 62e2b7d71985d127e63ce983de318f218cbe20d6 /2024/08-Resonant_Collinearity/first.hs | |
parent | 2024-02 in factor (diff) | |
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2024-08 in haskell
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-rw-r--r-- | 2024/08-Resonant_Collinearity/first.hs | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/2024/08-Resonant_Collinearity/first.hs b/2024/08-Resonant_Collinearity/first.hs new file mode 100644 index 0000000..5c611ef --- /dev/null +++ b/2024/08-Resonant_Collinearity/first.hs @@ -0,0 +1,57 @@ +-- requires cabal install --lib megaparsec parser-combinators heap vector +module Main (main) where + +import Control.Monad (void, when) +import qualified Data.Set as S +import Data.Void (Void) +import Text.Megaparsec +import Text.Megaparsec.Char + +exampleExpectedOutput = 14 + +data Antenna = Antenna Char Int Int deriving Show +type Input = [Antenna] +type Input' = (Int, Input) + +type Parser = Parsec Void String + +parseAntenna :: Parser Antenna +parseAntenna = do + (SourcePos _ y x) <- getSourcePos + c <- alphaNumChar + pure $ Antenna c (unPos x - 1) (unPos y - 1) + +skipDots :: Parser () +skipDots = skipMany (char '.' <|> char '\n') + +parseInput' :: Parser Input +parseInput' = some (skipDots *> parseAntenna <* skipDots) <* 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 (length (lines input), input') + +type Antinodes = S.Set (Int, Int) + +compute :: Input' -> Int +compute (size, input) = S.size . S.filter valid $ compute' input S.empty + where + valid (x, y) = x >= 0 && x < size && y >= 0 && y < size + compute' :: Input -> Antinodes -> Antinodes + compute' [_] acc = acc + compute' (x:xs) acc = compute' xs . S.unions $ acc : map (antinodes x) xs + antinodes :: Antenna -> Antenna -> Antinodes + antinodes (Antenna c1 x1 y1) (Antenna c2 x2 y2) | c1 /= c2 = S.empty + | otherwise = let (dx, dy) = (x2 - x1, y2 - y1) + in S.fromList [(x1 - dx, y1 - dy) , (x2 + dx, y2 + dy)] + +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 |