]> Hi algorithmers, Given two sets A and B, I want to calculate A\B _and_ B\A. The sets are represented by lists. without using an order to sort the lists, is there something better than the following (O(n^2)) ? << let omem a = let rec aux acc = function | [] -> None | a'::q when a=a' -> Some (List.rev_append acc q) | a'::q -> aux (a'::acc) q in aux [] let xor x = let rec aux (a',b') = function | la, [] -> List.rev_append a' la, b' | [], lb -> a', List.rev_append b' lb | a::qa, b::qb when a=b -> aux (a',b') (qa,qb) | a::qa, b::qb -> match omem a qb, omem b qa with | None, None -> aux (a::a', b::b') (qa, qb ) | Some qb', None -> aux ( a', b::b') (qa, qb') | None, Some qa' -> aux (a::a', b') (qa',qb ) | Some qb', Some qa' -> aux ( a', b') (qa',qb') in aux ([],[]) x >> # xor ([4;1;6;2;8],[3;9;5;2;8;1;7]);; - : int list * int list = ([6; 4], [3; 9; 5; 7]) with an order, is there something better than (O(n*ln n)) : * sort the two lists, * "merge" them to extract the result ? what's the complexity of <Set.Make(M).diff>, from the standard library ? thanks, damien ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners