X-Git-Url: https://git.njae.me.uk/?p=advent-of-code-20.git;a=blobdiff_plain;f=advent24%2Fsrc%2Fadvent24.hs;fp=advent24%2Fsrc%2Fadvent24.hs;h=d9bcc928c3bbf7abeb55ec9058e9156bb4064636;hp=0000000000000000000000000000000000000000;hb=d51325ae0b835dd8928bd136d625db22741b4e97;hpb=5072f95356c17607722dddb918805ea1c48b8332

diff --git a/advent24/src/advent24.hs b/advent24/src/advent24.hs
new file mode 100644
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+++ b/advent24/src/advent24.hs
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+-- import Debug.Trace
+
+import Data.Text (Text)
+-- import qualified Data.Text as T
+import qualified Data.Text.IO as TIO
+
+import Data.Attoparsec.Text hiding (take)
+-- import Data.Attoparsec.Combinator
+-- import Control.Applicative
+-- import Control.Applicative.Combinators
+
+import qualified Data.Set as S
+import Linear (V2(..), (^+^))
+-- import Data.Semigroup
+-- import Data.Monoid
+
+
+data Direction = NE | E | SE | SW | W | NW
+  deriving (Show, Eq, Enum, Bounded)
+
+type Tile = V2 Int -- x, y
+type Grid = S.Set Tile
+
+instance Semigroup Int where
+  (<>) = (+)
+
+instance Monoid Int where
+  mempty = 0
+
+main :: IO ()
+main = 
+    do text <- TIO.readFile "data/advent24.txt"
+       let walks = successfulParse text
+       let grid0 = foldr flipTile S.empty walks
+       print $ part1 grid0
+       print $ part2 grid0
+
+part1 grid0 = S.size grid0
+part2 grid0 = S.size $ (iterate update  grid0) !! 100
+
+delta :: Direction -> Tile
+delta NE = V2  1  0
+delta E  = V2  0  1
+delta SE = V2 -1  1
+delta SW = V2 -1  0
+delta W  = V2  0 -1
+delta NW = V2  1 -1
+
+
+flipTile :: Tile -> Grid -> Grid
+flipTile tile tiles 
+  | tile `S.member` tiles = S.delete tile tiles
+  | otherwise = S.insert tile tiles
+
+
+neighbourSpaces :: Tile -> Grid
+neighbourSpaces here = S.fromList $ map nbrSpace [minBound .. maxBound] -- [NE .. NW]
+  where nbrSpace d = here ^+^ (delta d)
+
+countOccupiedNeighbours :: Tile -> Grid -> Int
+countOccupiedNeighbours cell grid = 
+  S.size $ S.intersection grid $ neighbourSpaces cell
+
+tileBecomesWhite :: Grid -> Tile -> Bool
+tileBecomesWhite grid cell = black && ((nNbrs == 0) || (nNbrs > 2))
+  where black = cell `S.member` grid
+        nNbrs = countOccupiedNeighbours cell grid
+
+tileBecomesBlack :: Grid -> Tile -> Bool
+tileBecomesBlack grid cell = white && (nNbrs == 2)
+  where white = cell `S.notMember` grid
+        nNbrs = countOccupiedNeighbours cell grid
+
+update :: Grid -> Grid
+update grid = (grid `S.union` newBlacks) `S.difference` newWhites
+  where neighbours = (S.foldr mergeNeighbours S.empty grid) `S.difference` grid
+        mergeNeighbours cell acc = S.union acc $ neighbourSpaces cell
+        newWhites = S.filter (tileBecomesWhite grid) grid
+        newBlacks = S.filter (tileBecomesBlack grid) neighbours
+
+
+-- Parse the input file
+
+tilesP = tileP `sepBy` endOfLine
+tileP = foldMap delta <$> many1 stepP
+
+stepP = choice [neP, nwP, seP, swP, eP, wP]
+
+neP = "ne" *> pure NE
+nwP = "nw" *> pure NW
+seP = "se" *> pure SE
+swP = "sw" *> pure SW
+eP  = "e"  *> pure E
+wP  = "w"  *> pure W
+
+-- successfulParse :: Text -> [Tile]
+successfulParse input = 
+  case parseOnly tilesP input of
+    Left  _err -> [] -- TIO.putStr $ T.pack $ parseErrorPretty err
+    Right tiles -> tiles