day12, simple recursive solution

now to memoize it…

2023/day12/day12.hs

@@ -1,5 +1,4 @@
 import Control.Arrow
-import Control.Monad
 import Data.List
 
 main :: IO ()
@@ -9,32 +8,20 @@ parse :: String -> (String, [Int])
 parse = second (read . ('[' :) . (++ "]") . tail) . break (== ' ')
 
 day12 :: [(String, [Int])] -> Int
-day12 = sum . map (length . genArrangements)
+day12 = sum . map (uncurry (countArr 0))
 
 part2ify :: (String, [Int]) -> (String, [Int])
 part2ify (s, xs) = (intercalate "?" $ replicate 5 s, concat $ replicate 5 xs)
 
-genMin :: [Int] -> [String]
-genMin = foldr (\x -> (:) (replicate x '#' ++ ".")) []
-
-genDots :: Int -> Int -> [[Int]]
-genDots n x = filter (\xs -> sum xs == x) $ replicateM n [0 .. x]
-
-buildMaxeds :: [String] -> [[Int]] -> [String]
-buildMaxeds ss = map (build ss)
-
-build :: [String] -> [Int] -> String
-build [] [x] = replicate x '.'
-build (s:ss) (x:xs) = replicate x '.' ++ s ++ build ss xs
-
-genArrangements :: (String, [Int]) -> [String]
-genArrangements (s, xs) = filter f $ buildMaxeds (genMin xs) (genDots w l)
-  where
-    f x = and (zipWith wEq s x)
-    w = succ $ length xs
-    l = length s - sum xs - pred (length xs)
-
-wEq :: Char -> Char -> Bool
-wEq _ '?' = True
-wEq '?' _ = True
-wEq c1 c2 = c1 == c2
+countArr :: Int -> String -> [Int] -> Int
+countArr 0 [] [] = 1
+countArr _ [] [] = 0
+countArr _ ss [] = fromEnum $ not $ any (=='#') ss
+countArr streak [] [i] = fromEnum $ streak==i
+countArr streak (s:ss) (i:is)
+  | s=='.' && streak == 0 = countArr 0 ss (i:is)
+  | s=='.' && streak == i = countArr 0 ss is
+  | s=='.' = 0
+  | s=='#' = countArr (succ streak) ss (i:is)
+  | s=='?' = countArr streak ('.':ss) (i:is) + countArr streak ('#':ss) (i:is)
+countArr _ _ _ = 0