diff --git a/day8.hs b/day8.hs new file mode 100644 index 0000000..be5c322 --- /dev/null +++ b/day8.hs @@ -0,0 +1,52 @@ +import Data.Char (digitToInt) +import Data.List (transpose, zip4, zipWith4) + +-- a fun approach, not necessarily the fastest (or cleanest (or smartest)) + +main :: IO () +main = do + input <- map (map digitToInt) . lines <$> readFile "day8.in" + let (e, w, n, s) = trees input + let obscured = zipWith4 zip4 e w n s + putStr "Q1: " + print $ + length $ + filter + (not . (\((w, _), (x, _), (y, _), (z, _)) -> w && y && x && z)) + $ concat obscured + putStr "Q2: " + print $ + maximum $ + map (\((_, w), (_, x), (_, y), (_, z)) -> w * x * y * z) $ + concat obscured + +type Forest = [[(Bool, Int)]] + +trees :: [[Int]] -> (Forest, Forest, Forest, Forest) +trees input = + ( trees' input, + map reverse $ trees' $ map reverse input, + transpose $ trees' $ transpose input, + reverse $ transpose $ trees' $ transpose $ reverse input + ) -- (east, west, north, south) traversals + where + trees' :: [[Int]] -> Forest + trees' = + foldr + ( \x xs -> + let (_, dist) = + foldr + ( \(cur, y) ((old, m), ys) -> + ( if y > m then (cur, y) else (old, m), + ( y <= m, + let s = length $ takeWhile (< y) $ reverse $ take cur x + in if s == cur then s else s + 1 + ) : + ys + ) + ) + ((-1, -1), []) + (zip [0 ..] x) + in dist : xs + ) + []