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-rw-r--r--2023/17-Clumsy_Crucible/second.hs109
1 files changed, 109 insertions, 0 deletions
diff --git a/2023/17-Clumsy_Crucible/second.hs b/2023/17-Clumsy_Crucible/second.hs
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+++ b/2023/17-Clumsy_Crucible/second.hs
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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 = 94
+
+type Line = VU.Vector Int
+type Input = V.Vector Line
+
+type Parser = Parsec Void String
+
+parseLine :: Parser Line
+parseLine = do
+ line <- some (C.digitToInt <$> digitChar) <* eol
+ return $ VU.generate (length line) (line !!)
+
+parseInput' :: Parser Input
+parseInput' = do
+ line <- some parseLine <* eof
+ return $ V.generate (length line) (line !!)
+
+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'
+
+data Heading = NS | EW deriving (Eq, Show)
+data Position = Position Int Int Int Heading deriving (Show) -- cost x y heading
+instance Ord Position where
+ compare (Position c1 _ _ _) (Position c2 _ _ _) = c1 `compare` c2
+instance Eq Position where
+ (Position c1 _ _ _) == (Position c2 _ _ _) = c1 == c2
+type Candidates = H.MinHeap Position
+type CostsState = M.Map (Int,Int) (Int, Int) -- (x, y) (NSCost, EWCost)
+
+step :: Input -> CostsState -> Position -> [Position]
+step input costs (Position cost x y h) = L.concat [next 1 1 0, next (-1) (-1) 0]
+ where
+ next :: Int -> Int -> Int -> [Position] -- diff increment costchange
+ next 11 _ _ = []
+ next (-11) _ _ = []
+ next d i costChange = case heatLoss of
+ Just hl -> if improvement hl then (Position (cost + costChange + hl) x' y' h') : next (d+i) i (costChange + hl)
+ else next (d+i) i (costChange + hl)
+ Nothing -> []
+ where
+ h' | h == NS = EW
+ | otherwise = NS
+ x' | h' == NS = x
+ | otherwise = x + d
+ y' | h' == NS = y + d
+ | otherwise = y
+ improvement :: Int -> Bool
+ improvement hl | d < 4 && d > -4 = False
+ | otherwise = case M.lookup (x', y') costs of
+ Just (h1, h2) -> case h' of
+ NS -> cost + hl < h1
+ EW -> cost + hl < h2
+ Nothing -> undefined -- should not happen, we catch out of bound when looking for heatLoss
+ heatLoss :: Maybe Int
+ heatLoss = case input V.!? y' of
+ Just line -> line VU.!? x'
+ Nothing -> Nothing
+
+compute :: Input -> Int
+compute input = compute' startingCosts startingCandidates
+ where
+ compute' :: CostsState -> Candidates -> Int
+ compute' costs candidates | x == size - 1 && y == size - 1 = cost
+ | improvement = compute' costs' (H.union candidates' (H.fromList $ step input costs position))
+ | otherwise = compute' costs candidates'
+ where
+ candidates' = H.drop 1 candidates
+ costs' = M.insert (x, y) (if h == NS then (cost, snd state) else (fst state, cost)) costs
+ improvement | h == NS = cost < fst state
+ | otherwise = cost < snd state
+ position@(Position cost x y h) = head $ H.take 1 candidates
+ state = costs M.! (x, y)
+ infinity = maxBound :: Int
+ startingCandidates = H.fromList [Position 0 0 0 h|h <- [NS, EW]] :: Candidates
+ startingCosts = M.fromList [((x, y), (infinity, infinity))|x<-[0..size], y<-[0..size]]
+ size = V.length input
+
+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