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