import qualified Data.IntMap.Strict as M filterSum :: Int -> M.IntMap Int -> Int filterSum n subMap = let filterMap = M.filterWithKey (\k _ -> k <= n) subMap in M.foldr (+) 0 filterMap getSubmap :: Int -> M.IntMap (M.IntMap Int) -> M.IntMap Int getSubmap k numMap = M.findWithDefault undefined k numMap insertSubmap :: Int -> M.IntMap (M.IntMap Int) -> M.IntMap (M.IntMap Int) insertSubmap n numMap = let getFilterSumInsert k subMap = M.insert k (filterSum k (getSubmap (n-k) numMap)) subMap subMap = foldr getFilterSumInsert M.empty [n, n-1..1] in M.insert n subMap numMap createNummap :: Int -> M.IntMap (M.IntMap Int) createNummap bound = let initialMap = M.fromList [(0, M.fromList [(0, 1)])] in foldr insertSubmap initialMap [bound, bound-1..1] main = print $ let bound = 100 ways = filterSum bound $ M.findWithDefault undefined bound $ createNummap bound in ways - 1