Slow correct

app/12.hs

@@ -2,14 +2,38 @@
 module Main where
 
 import Data.Functor
+import Data.Matrix hiding (trace)
+import Data.List
+import Debug.Trace
 
-parse = undefined
+parse :: String -> Matrix Char
+parse = fromLists . lines
 
-solve1 = undefined
+getGroup :: (Int,Int) -> Matrix Char -> [(Int,Int)] -> [(Int,Int)]
+getGroup p@(i,j) s v
+  | p `elem` v = v
+  | otherwise = let e = getElem i j s in
+      nub . (p:) $ filter((== Just e) . flip (uncurry safeGet) s) [(i,j+1),(i,j-1),(i+1,j),(i-1,j)] >>= \p' -> getGroup p' s (p:v)
+  where
 
+groups :: Matrix Char -> [[(Int,Int)]]
+groups s = nub $ go [(i,j) | i <- [1 .. nrows s], j <- [1 .. ncols s]] []
+  where go :: [(Int,Int)] -> [[(Int,Int)]] -> [[(Int,Int)]]
+        go [] v = v
+        go (x:xs) v
+          | any (x `elem`) v = go xs v
+          | otherwise = go xs (getGroup x s []:v)
+
+perimeter :: [(Int,Int)] -> Int
+perimeter s = length $ s >>= \(i,j) -> [(i,j+1),(i,j-1),(i+1,j),(i-1,j)] \\ s
+
+solve1 :: Matrix Char -> Int
+solve1 s = let g = groups s; p = perimeter <$> g in sum $ zipWith (*) (length <$> g) p
+
+solve2 :: Matrix Char -> Int
 solve2 = undefined
 
 main :: IO ()
-main = readFile "inputs/12" <&> parse >>= \i ->
+main = readFile "inputs/12.example" <&> parse >>= \i ->
        print (solve1 i) >>
        print (solve2 i)