Day 9 finished. Finally.

src/AOC-09b.hs

 module Main where
 
-import Data.Array
-import Data.List
+import Data.Array ( Ix(range, inRange), Array, array, (!), bounds )
+import Data.List ( sort )
 import qualified Data.Set as S
 import Data.Set (Set)
 
@@ -36,32 +36,22 @@ lowPoints arr = filter (isLowPoint arr) . range . bounds $ arr
 -- This code is wrong for the interpretation of a basin given by
 -- the problem.
 
-basin :: Array (Int,Int) Int -> (Int,Int) -> Set (Int,Int)
-basin arr pos = search (S.singleton pos) where
-  frontier :: Set (Int,Int) -> Set (Int,Int)
-  frontier pts = expansion `S.difference` pts where
-    expansion = S.fromList . foldr (\pt rest -> neighbors arr pt ++ rest) [] $ pts
-  search :: S.Set (Int,Int) -> S.Set (Int,Int)
-  search pts
-    | not . S.null $ newpoints = search (pts `S.union` newpoints)
-    | otherwise = pts
-    where
-      newpoints = S.fromList 
-                  [pt | pt <- S.toList (frontier pts)
-                      , flowPoint pt
-                      , S.fromList (flowsFrom pt) `S.isSubsetOf` pts
-                  ]
-      flowsFrom pt = [p | p <- neighbors arr pt
-                        , arr ! p < arr ! pt]
-      flowPoint pt = arr ! pt /= 9 && all ((/= arr ! pt) . (arr !)) (neighbors arr pt)
+basins :: Array (Int,Int) Int -> [Set (Int,Int)]
+basins heightMap = findBasins viablePoints where
+  viablePoints = S.fromList . filter ((<9) . (heightMap !)) . range . bounds $ heightMap
+  findBasins s
+    | S.null s = []
+    | otherwise = 
+        let foundPoints = searchFrom [S.findMin s] S.empty
+        in foundPoints : findBasins (s `S.difference` foundPoints)
+  searchFrom :: [(Int,Int)] -> Set (Int,Int) -> Set (Int,Int)
+  searchFrom [] visited = visited
+  searchFrom (p:ps) pts
+    | p `S.member` pts || heightMap ! p == 9 = searchFrom ps pts
+    | otherwise = searchFrom (neighbors heightMap p ++ ps) (S.insert p pts)
+
 
 main :: IO ()
 main = do
   heightMap <- makeHeightMap <$> readFile "data/heightMap.txt"
-  putStr . show . take 3 . reverse . sort . map S.size $ basin heightMap <$> lowPoints heightMap
-
-{- failed answers:
-
-414960
-
--}
\ No newline at end of file
+  print . product . take 3 . reverse . sort . map S.size . basins $ heightMap

src/AOC-12a.hs

@@ -45,7 +45,7 @@ paths cm = iter (Small "start") (S.singleton (Small "start")) [Small "start"] wh
   iter :: Cave -> Set Cave -> [Cave] -> [[Cave]]
   iter (Small "end") _ path = [reverse path]
   iter cave visited path = do
-    next <- filter (`notElem` visited) . (cm !) $ cave
+    next <- cm ! cave
     guard $ next `notElem` visited
     case next of
       Big _ -> iter next visited (next : path)
@@ -61,4 +61,3 @@ processCaveFile file = do
 main :: IO ()
 main = do
   processCaveFile "data/caves.txt"
-

src/AOC-12b.hs

@@ -65,4 +65,3 @@ processCaveFile file = do
 main :: IO ()
 main = do
   processCaveFile "data/caves.txt"
-