From 538211604edf32dc3d7ce9a0a2d82f3851557733 Mon Sep 17 00:00:00 2001 From: Tom Smeding <tom@tomsmeding.com> Date: Sun, 8 Dec 2024 22:25:54 +0100 Subject: 6 Part 2 is very slow, but meh? --- 2024/6.hs | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) create mode 100644 2024/6.hs (limited to '2024/6.hs') diff --git a/2024/6.hs b/2024/6.hs new file mode 100644 index 0000000..6fe65bf --- /dev/null +++ b/2024/6.hs @@ -0,0 +1,41 @@ +import Data.List (findIndex, find) +import Data.Maybe (isJust, fromJust, isNothing) +import qualified Data.Set as Set +import qualified Data.Array as A + +main :: IO () +main = do + let bd `at` (x, y) = bd A.! (y, x) + let inBounds bd (x, y) = + let (_, (h, w)) = A.bounds bd + in x >= 0 && y >= 0 && x <= w && y <= h + let (x, y) +. (dx, dy) = (x + dx, y + dy) + let rot (dx, dy) = (-dy, dx) + let walk :: A.Array (Int, Int) Char + -> (Int, Int) -> (Int, Int) + -> Set.Set ((Int, Int), (Int, Int)) + -> Maybe (Set.Set ((Int, Int), (Int, Int))) + walk bd p dir seen + | not (inBounds bd p) = Just seen + | (p, dir) `Set.member` seen = Nothing + | otherwise = + let p' = p +. dir + in if inBounds bd p' && bd `at` p' == '#' + then walk bd p (rot dir) seen + else walk bd p' dir (Set.insert (p, dir) seen) + + bd' <- lines <$> getContents + let Just (Just initx, inity) = find (isJust . fst) (zip (map (findIndex (== '^')) bd') [0..]) + let makeBd = A.listArray ((0, 0), (length bd' - 1, length (head bd') - 1)) . concat + + let normalPath = Set.toList $ Set.map fst $ fromJust $ walk (makeBd bd') (initx, inity) (0, -1) mempty + print $ length normalPath + + let freePositions = normalPath + let makeObsBd (ox, oy) = makeBd $ zipWith fixrow [0..] bd' + where fixrow y row | y == oy = zipWith fix [0..] row + | otherwise = row + fix x c | x == ox = '#' + | otherwise = c + let valid p = p /= (initx, inity) && isNothing (walk (makeObsBd p) (initx, inity) (0, -1) mempty) + print $ length (filter valid freePositions) -- cgit v1.2.3-70-g09d2