feat: take a stab on day 9 part 2

app/Day9.hs

@@ -1,6 +1,8 @@
 module Main where
 
 import Data.List (uncons)
+import Data.Map.Strict (Map)
+import Data.Map.Strict qualified as M
 import Data.Maybe (mapMaybe)
 import Data.Set (Set)
 import Data.Set qualified as S
@@ -38,6 +40,14 @@ combine as = S.toList $ foldl' (go as) S.empty as
 part1 :: String -> Int
 part1 = maximum . map (uncurry area) . combine . parse
 
+-- | Idea: The red tiles form corners in a shape where the green tiles
+-- are the walls. In order to be able to create a rectangle the
+-- opposite tiles needs to be "visible" to each other, i.e. there
+-- cannot be a wall tile in the way.
+--
+-- Create the shape, for each red tile create a beam to every other
+-- red tile, if they are unobstructed store the area. Pick the
+-- greatest area.
 part2 :: String -> Int
 part2 = error "Not implemented"