added contiguous regions finder

Author: mstksg

src/AOC/Common/Point.hs

@@ -39,6 +39,7 @@ module AOC.Common.Point (
  , boundingBox'
  , inBoundingBox
  , minCorner, minCorner'
+ , contiguousRegions
  , shiftToZero
  , shiftToZero'
  , parseAsciiMap
@@ -171,6 +172,26 @@ fullNeighbsSet p = S.fromDistinctAscList $
  , d /= pure 0
  ]
 
+-- | Find contiguous regions by cardinal neighbors
+contiguousRegions
+ :: Set Point
+ -> Set (Set Point)
+contiguousRegions = startNewPool S.empty
+ where
+ startNewPool seenPools remaining = case S.minView remaining of
+ Nothing -> seenPools
+ Just (x, xs) ->
+ let (newPool, remaining') = fillUp (NES.singleton x) S.empty xs
+ in startNewPool (S.insert newPool seenPools) remaining'
+ fillUp boundary internal remaining = case NES.nonEmptySet newBoundary of
+ Nothing -> (newInternal, remaining)
+ Just nb -> fillUp nb newInternal newRemaining
+ where
+ edgeCandidates = foldMap' cardinalNeighbsSet boundary `S.difference` internal
+ newBoundary = edgeCandidates `S.intersection` remaining
+ newInternal = internal `S.union` NES.toSet boundary
+ newRemaining = remaining `S.difference` edgeCandidates
+
 memoPoint :: Memo Point
 memoPoint = Memo.wrap (uncurry V2) (\(V2 x y) -> (x, y)) $
  Memo.pair Memo.integral Memo.integral