Day 03 - preliminary solution using lists; will implement using Map/Set/etc. later.

app/Main.hs

@@ -30,4 +30,4 @@ import qualified Day24
 import qualified Day25
 
 main :: IO ()
-main = Day02.main
+main = Day03.main

package.yaml

@@ -22,6 +22,7 @@ description:         Please see the README on GitHub at <https://github.com/iona
 dependencies:
 - base >= 4.7 && < 5
 - containers
+- text
 
 library:
   source-dirs: src

src/Day03.hs

@@ -1,6 +1,36 @@
 module Day03 (main) where
 
+import Data.Text (split, pack, unpack)
+
+type Claim  = (Int, Int, Int, Int, Int) -- id, left, top, width, height
+(%)  = mod
+(//) = div
+
+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)
+
+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
+
+part1 :: [Claim] -> Int
+part1 claims = length . filter id . map ((> 1) . claimCount claims) $ [0 .. 1000 * 1000 - 1]
+    
+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
+
 main :: IO ()
 main = do
-    input <- readFile "input/03.txt"
-    print input
+    input <- map parse . lines <$> readFile "input/03.txt"
+    print $ part1 input
+    print $ part2 input