On Fri, Jan 13, 2006 at 01:18:35PM +0000, Duncan Coutts wrote:
I've been looking around (unsuccessfully) for an efficient data structure to implement a sequence data type with indexed insert/delete/lookup.
lookup :: Sequence a -> Int -> Maybe a insert :: Sequence a -> Int -> a -> Sequence a delete :: Sequence a -> Int -> Sequence a
Have a look at Data.Sequence (in CVS/darcs version), docs at http://www.haskell.org/ghc/dist/current/docs/libraries/base/Data-Sequence.ht... insert and delete aren't provided, but are easily derived: insert :: Seq a -> Int -> a -> Seq a insert xs i x = front >< x <| back where (front, back) = splitAt i xs delete :: Seq a -> Int -> Seq a delete xs i = front >< drop 1 back where (front, back) = splitAt i xs (where splitAt and drop are the sequence versions). Each of the three operations takes O(log(min(i,n-i))) time.