Hi again, hoping to further increase performance i've decided to calculate the distances between all points ahead of time and store the distance values in a map of maps. Because of the symmetry of the matrix this should work in O(0.5*n^2). Could you please take a look at the code and tell me if this would be the way to go? I fear that i might actually loose performance due to the lookuptime of the treemap compared to recalculating the distance between two points? Thank you very much :) import qualified Data.Map as Map data Point a = Pt a a deriving (Show, Eq, Ord) manhattan (Pt x y) (Pt x' y') = abs (x' - x) + abs (y' - y) dist' :: Num a => Point a -> [Point a] -> [(Point a, a)] dist' p [] = [] dist' p l = zip l (map (manhattan p) l) dist :: (Num a, Ord a) => Point a -> [Point a] -> Map.Map (Point a) a dist p l = Map.fromList (dist' p l) distmatrix :: (Num a, Ord a) => [Point a] -> Map.Map (Point a) (Map.Map (Point a) a) distmatrix (p:[]) = Map.empty distmatrix (p:ps) = Map.insert p (dist p ps) (distmatrix ps) getdist' :: (Num a, Ord a) => Point a -> Point a -> Map.Map (Point a) (Map.Map (Point a) a) -> a getdist' p1 p2 dm = (dm Map.! p1) Map.! p2 getdist :: (Num a, Ord a) => Point a -> Point a -> Map.Map (Point a) (Map.Map (Point a) a) -> a getdist p1 p2 dm | Map.member p1 dm = getdist p1 p2 dm | otherwise = getdist' p2 p1 dm