50 lines
2.3 KiB
Haskell
50 lines
2.3 KiB
Haskell
module Day8.Puzzle2 (day8_2) where
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import Data.List (uncons)
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import Data.Maybe (fromJust)
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import Control.Applicative
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import Data.Set (fromList)
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import Data.Bifunctor (bimap)
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type Freq = Char
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type Coords = (Int, Int)
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data Antenna = Antenna { frequency :: Freq
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, coordinates :: Coords
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} deriving (Show, Eq)
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readAntenna :: Freq -> Coords -> Antenna
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readAntenna freq coords = Antenna {frequency=freq, coordinates=coords}
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getAntennas :: [String] -> [Antenna]
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getAntennas grid = concat . getZipList $ getAntennasRow <$> ZipList [0..] <*> ZipList grid
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where getAntennasRow n row = [ readAntenna x (n, y) | (x, y) <- zip row [0..], x /= '.' ]
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isInside :: Coords -> Int -> Int -> Bool
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isInside c x y = fst c >= 0 && fst c < x && snd c >= 0 && snd c < y
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generateCoords :: Coords -> Coords -> [Coords]
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generateCoords c offset = scanl shiftCoords c (repeat offset)
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where shiftCoords x = bimap (fst x +) (snd x +)
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getAntinodes :: Antenna -> Antenna -> Int -> Int -> [Coords]
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getAntinodes a b maxX maxY = let xa = fst $ coordinates a
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ya = snd $ coordinates a
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xb = fst $ coordinates b
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yb = snd $ coordinates b
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distX = xa - xb
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distY = ya - yb
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in if frequency a /= frequency b || coordinates a == coordinates b
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then []
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else filter (\c -> isInside c maxX maxY) [(2 * xa - xb, 2 * ya - yb), (2 * xb - xa, 2 * yb - ya)]
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++ takeWhile (\c -> isInside c maxX maxY) (generateCoords (coordinates a) (distX, distY))
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++ takeWhile (\c -> isInside c maxX maxY) (generateCoords (coordinates b) (-distX, -distY))
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day8_2 :: IO ()
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day8_2 = do
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contents <- lines <$> readFile "input/day8.txt"
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let antennas = getAntennas contents
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x = length contents
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y = length $ fst . fromJust $ uncons contents
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antinodes = fromList $ concat [ getAntinodes a b x y | a <- antennas, b <- antennas, a /= b, frequency a == frequency b ]
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putStrLn $ "Day 8, Puzzle 2 solution: " ++ show (length antinodes)
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