]> Oleg wrote: > On Thursday 05 December 2002 03:24 pm, Issac Trotts wrote: > > List.concat (List.map to_list2 strs);; > > ^^^^^^^^^ > > > > 2) What is the complexity of your function f ? > > > > The new ones have linear time complexity w.r.t. the number of > > characters. The old one has quadratic time complexity. > > Issac > > I haven't analyzed your whole functions, but List.flatten'ing alone is > O(S*L^2), so while it may be linear WRT the number of characters in one > string, it's not necessarily linear WRT the total number of characters. See > my version of f for O(L*S) time. > > Cheers > Oleg Thanks for pointing this out. Here's flatten, from list.ml: let rec flatten = function [] -> [] | l::r -> l @ flatten r let concat = flatten Here's (@), from pervasives.ml : let rec (@) l1 l2 = match l1 with [] -> l2 | hd :: tl -> hd :: (tl @ l2) If the given list has L elements, each with S items, then flatten should O((L*S)*L) = O(S*L^2) time, since you have to keep on churning through every single element in the ever-expanding l at every recursive flatten call. That's too bad. Here's an experiment I tried: $ cat ftime.ml let rec make_list_of_lists = function | 0 -> [] | n -> [1;2;3;4;5;6;7;8] :: make_list_of_lists(n-1) let _ = let n = int_of_string(Sys.argv.(1)) in let lol = make_list_of_lists n in ignore(List.flatten(lol)) ;; $ ocamlopt -o ftime ftime.ml $ for (( i=0; $i<100; i++ )) do /usr/bin/time -o data -a -f "%U" ./ftime "$i"000 done $ gnuplot > plot 'data' I guess it looks linear because of the small input size. This gives me the impression that List.flatten is practical, at least for small data sets. Issac ------------------- 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