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-rw-r--r--2023/18-Lavaduct_Lagoon/second.hs74
1 files changed, 74 insertions, 0 deletions
diff --git a/2023/18-Lavaduct_Lagoon/second.hs b/2023/18-Lavaduct_Lagoon/second.hs
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+-- requires cabal install --lib megaparsec parser-combinators heap vector text
+module Main (main) where
+
+import Control.Applicative.Permutations
+import Control.Monad (void, when)
+import Data.Bifunctor (bimap)
+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.Text as T
+import qualified Data.Text.Read as T
+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 = 952408144115
+
+data Heading = U | D | L | R deriving (Eq, Show)
+data Line = Line Int Heading
+type Input = [Line]
+
+type Parser = Parsec Void String
+
+parseHeading :: Parser Heading
+parseHeading = char '3' $> U
+ <|> char '1' $> D
+ <|> char '2' $> L
+ <|> char '0' $> R
+
+parseLine :: Parser Line
+parseLine = Line <$> (letterChar *> space *> some digitChar *> string " (#" *> (fst . fromRight (0, T.pack "") . T.hexadecimal . T.pack <$> count 5 alphaNumChar))
+ <*> (parseHeading <* 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'
+
+pick_theorem :: [(Int, Int)] -> Int
+pick_theorem vertices = 1 + perimeter `div` 2 + (abs . (`div` 2) . sum . zipWith crossProduct vertices $ tail vertices)
+ where crossProduct (x1, y1) (x2, y2) = y1 * x2 - x1 * y2
+ dist (x1, y1) (x2, y2) = abs (x1 - x2) + abs (y1 - y2)
+ perimeter = sum . zipWith dist vertices $ tail vertices
+
+compute :: Input -> Int
+compute input = pick_theorem $ (0, 0) : L.foldl' coords [(0, 0)] input
+ where
+ coords :: [(Int, Int)] -> Line -> [(Int, Int)]
+ coords acc@((x, y):_) (Line l h) | h == U = (x, y - l):acc
+ | h == D = (x, y + l):acc
+ | h == L = (x - l, y):acc
+ | h == R = (x + l, y):acc
+
+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