Day 03 - now with IntMap!

README.md

@@ -10,7 +10,7 @@ To arrive at [⟨ortho|normal⟩](https://hilb.ert.space) as December comes.
 |-----|-------------|------------|
 | 01  | < 0.1       |
 | 02  | < 0.1       |
-| 03  |             |
+| 03  | ~ 2         |
 | 04  |             |
 | 05  |             |
 | 06  |             |

src/Day03.hs

@@ -1,33 +1,24 @@
 module Day03 (main) where
 
-import Data.Text (split, pack, unpack)
+import Data.Text (empty, split, pack, unpack)
+import Data.IntMap (IntMap, fromListWith, size, notMember)
+import qualified Data.IntMap as M (filter)
 
-type Claim  = (Int, Int, Int, Int, Int) -- id, left, top, width, height
-(%)  = mod
-(//) = div
+type Claim = (Int, [Int])
 
 parse :: String -> Claim
 parse str =
-    let i:l:t:w:h:[] = map (read . unpack) . tail . split (flip elem $ "#@,:x") . pack . filter (/= ' ') $ str
-    in  (i, l, t, w, h)
+    let i:l:t:w:h:[] = map (read . unpack) . filter (/= empty) . split (flip elem $ " #@,:x") . pack $ str
+    in  (i, [r * 1000 + c | r <- [t .. t + h - 1], c <- [l .. l + w - 1]])
 
-doesClaim :: Int -> Claim -> Bool
-doesClaim cell (_, left, top, width, height) =
-    let row = cell // 1000
-        col = cell %  1000
-    in  (row >= top) && (row < top + height) && (col >= left) && (col < left + width)
-
-claimCount :: [Claim] -> Int -> Int
-claimCount claims cell = length . filter (doesClaim cell) $ claims
+overlapMap :: [Claim] -> IntMap Int
+overlapMap = M.filter (> 1) . fromListWith (+) . (flip zip) (repeat 1) . concat . map snd
 
 part1 :: [Claim] -> Int
-part1 claims = length . filter id . map ((> 1) . claimCount claims) $ [0 .. 1000 * 1000 - 1]
+part1 = size . overlapMap
 
-part2 :: [Claim] -> Claim
-part2 claims = filterOverlaps 0 claims
-    where filterOverlaps cell acc =
-            let newAcc = if claimCount claims cell > 1 then filter (not . doesClaim cell) acc else acc
-            in  if length newAcc == 1 then head newAcc else filterOverlaps (cell + 1) newAcc
+part2 :: [Claim] -> Int
+part2 claims = fst . head . filter (all (flip notMember $ overlapMap claims) . snd) $ claims
 
 main :: IO ()
 main = do