View difference between Paste ID: nBF8TcrA and G2MKxkrT

 import Data.Char (ord)
-import qualified Data.Map as M
+import qualified Data.Set as S
 import qualified Data.Vector as V
 
-type Done = M.Map Coord Bool
+
 type Done = S.Set Coord
 type Todo = [Coord]
 
 main = putStrLn $ show n
-n = loop 0 [(0,0)] M.empty
+
 n = loop 0 [(0,0)] S.empty
 
 loop :: Int -> Todo -> Done -> Int
-loop n (t:ts) d = loop (n + count t) (also t d ++ ts) (M.insert t True d)
+
 loop n (t:ts) d = loop (n + count t) (also t d ++ ts) (S.insert t d)
 
 count :: Coord -> Int
 count (0,0) = 1
 count (0,_) = 4
 count (_,0) = 4
 count (x,y) = if x == y then 4 else 8
 
-also c d = filter (\k -> M.notMember k d) $
+
 also c d = filter (\k -> S.notMember k d) $
            filter isAccessible $
            filter inQuadrant $
            next c
 
 isAccessible :: Coord -> Bool
 isAccessible (x,y) = sumDigits <= 19
-    sumDigits = sum1 x + sum1 y
+
     sumDigits = sums V.! x + sums V.! y
-    val x = ord x - ord '0'
+
 inQuadrant :: Coord -> Bool
 inQuadrant (x,y) = y <= x
 
 next :: Coord -> Todo
 next (x,y) = [(x+1,y), (x,y+1)]
-next (x,y) = [(x+1,y), (x,y+1)]
+
 sums :: V.Vector Int
 sums = V.generate 300 sum1
   where
     sum1 n = sum $ map val (show n)
     val x = ord x - ord '0'