10

1 files changed, 24 insertions, 0 deletions

diff --git a/2024/10.hs b/2024/10.hs
new file mode 100644
index 0000000..cbb291c
--- /dev/null
+++ b/2024/10.hs
@@ -0,0 +1,24 @@
+import qualified Data.Array as A
+import Data.Array (Array, (!))
+import Data.Foldable (toList)
+import qualified Data.Set as Set
+import Data.Bifunctor (bimap)
+
+amap :: A.Ix i => (i -> a -> b) -> Array i a -> Array i b
+amap f arr = A.listArray (A.bounds arr) (zipWith f (A.indices arr) (toList arr))
+
+main :: IO ()
+main = do
+  topo' <- map (map (read @Int . pure)) . lines <$> getContents
+  let w = length (head topo')
+  let h = length topo'
+  let topo = A.listArray ((0, 0), (w - 1, h - 1)) (concat topo')
+  let flood9 = amap (\i n -> if n == 9 then (Set.singleton i, 1::Int) else (mempty, 0)) topo
+  let inBounds (x, y) = 0 <= x && x < w && 0 <= y && y < h
+  let neighs (x, y) = filter inBounds [(x-1,y), (x+1,y), (x,y-1), (x,y+1)]
+  let stepdown mp =
+        amap (\i n -> bimap Set.unions sum $ unzip [mp ! p | p <- neighs i, topo ! p == n + 1]) topo
+  let flood = iterate stepdown flood9 !! 9
+  let (totscore, totrank) = bimap sum sum $ unzip $ map (\((s,n),_) -> (Set.size s, n)) $ filter (\(_,n) -> n == 0) $ zip (A.elems flood) (A.elems topo)
+  print totscore
+  print totrank