95 lines
3.4 KiB
Haskell
95 lines
3.4 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Applicative.Permutations
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import Control.Monad (void, when)
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import qualified Data.Char as C
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import Data.Either
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import Data.Functor
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import qualified Data.Heap as H
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import qualified Data.List as L
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import qualified Data.Map as M
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import Data.Maybe
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import qualified Data.Set as S
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import qualified Data.Vector as V
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import qualified Data.Vector.Unboxed as VU
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import Data.Void (Void)
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import Text.Megaparsec
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import Text.Megaparsec.Char
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import Debug.Trace
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exampleExpectedOutput = 62
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data Heading = U | D | L | R deriving (Eq, Show)
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data Line = Line Heading Int String
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type Input = [Line]
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type Parser = Parsec Void String
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parseHeading :: Parser Heading
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parseHeading = char 'U' $> U
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<|> char 'D' $> D
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<|> char 'L' $> L
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<|> char 'R' $> R
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parseLine :: Parser Line
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parseLine = Line <$> parseHeading <* space
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<*> (read <$> some digitChar) <* space
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<*> (string "(#" *> some alphaNumChar <* char ')' <* eol)
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parseInput' :: Parser Input
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parseInput' = some parseLine <* eof
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> error $ errorBundlePretty bundle
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Right input' -> return input'
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type Map = M.Map (Int, Int) Bool
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type Plan = (Map, Int, Int)
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compute :: Input -> Int
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compute input = xlen * ylen - M.size (M.filter not floodedPit) -- L.foldl' countLine 0 [ymin..ymax]
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where
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-- filling
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(xs, ys) = unzip $ M.keys trenches
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xmin = minimum xs - 1
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xmax = maximum xs + 1
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xlen = xmax - xmin + 1
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ymin = minimum ys - 1
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ymax = maximum ys + 1
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ylen = ymax - ymin + 1
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floodedPit = flood (xmin, ymin) trenches
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flood (x, y) m | x < xmin || x > xmax || y < ymin || y > ymax = m
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| M.member (x, y) m = m
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| otherwise = flood (x-1, y) $ flood (x+1, y) $ flood (x, y-1) $ flood (x, y+1) $ M.insert (x, y) False m
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---- digging
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(trenches, _, _) = L.foldl' digOne (M.singleton (0, 0) True, 0, 0) input
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digOne :: Plan-> Line -> Plan
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digOne (m, x, y) (Line h l _) = (digTrench m h l, x', y')
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where
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digTrench :: Map -> Heading -> Int -> Map
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digTrench m _ (-1) = m
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digTrench m U i = digTrench (M.insert (x, y-i) True m) U (i - 1)
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digTrench m D i = digTrench (M.insert (x, y+i) True m) D (i - 1)
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digTrench m L i = digTrench (M.insert (x-i, y) True m) L (i - 1)
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digTrench m R i = digTrench (M.insert (x+i, y) True m) R (i - 1)
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x' | h == U = x
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| h == D = x
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| h == L = x - l
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| h == R = x + l
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y' | h == U = y - l
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| h == D = y + l
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| h == L = y
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| h == R = y
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main :: IO ()
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main = do
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example <- parseInput "example"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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