1 files changed, 15 insertions(+), 6 deletions(-)

M 2023/16.hs

@@ 65,20 65,29 @@ step g (p@(x,y),d) = filter (\(p, _) -> Grid.inBounds g p) $
     (Just SplitterEW, East) -> [((x+1,y), d)]
     (Just SplitterEW, West) -> [((x-1,y), d)]
 
-partA :: Parse -> Int
-partA g = Set.size $ Set.map fst $ f Set.empty [((1,1), East)]
+energizedTiles :: Grid Thing -> Beam -> Int
+energizedTiles g = Set.size . Set.map fst . f Set.empty . flip (:) []
   where f vs [] = vs
         f vs (b:bs) = 
           let bs' = filter (\b' -> b' `Set.notMember` vs) $ step g b in
           let vs' = Set.insert b vs in
           f vs' (bs'++bs)
 
---partB :: Parse -> Parse
---partB = id
+partA :: Parse -> Int
+partA g = energizedTiles g ((1,1), East)
+
+partB :: Parse -> Int
+partB g =
+  let ((minX, minY), (maxX, maxY)) = Grid.bounds g in
+  maximum $ fmap (energizedTiles g) $
+     [((minX, y), East) | y <- [minY..maxY]]
+  ++ [((maxX, y), West) | y <- [minY..maxY]]
+  ++ [((x, minY), South) | x <- [minX..maxX]]
+  ++ [((x, maxY), North) | x <- [minX..maxX]]
 
 main :: IO ()
 main = with parser $ do
   run' "16.example" "a example" partA 46
   run' "16.input" "a input" partA 7210
-  --run "16.example" "b example" partB
-  --run "16.input" "b input" partB
+  run' "16.example" "b example" partB 51
+  run' "16.input" "b input" partB 7673