See also David Nolan's post: http://dosync.posterous.com/lispers-know-the-value-of-everything-and-the
Justin On Tuesday, August 9, 2011 6:02:00 PM UTC-4, pmbauer wrote: > > For the sieve, if performance matters, clojure's native data structures may > not be the best choice. > A mutable array of boolean primitives could be more apropos. > > (defn prime-sieve [^long n] > (let [^booleans sieve (make-array Boolean/TYPE (inc n))] > ...) > > ... using aset/aget to write/read sieve. > > On Tuesday, August 9, 2011 1:18:46 PM UTC-7, Chouser wrote: >> >> On Tue, Aug 9, 2011 at 12:50 PM, Kevin Sookocheff >> <kevin...@gmail.com> wrote: >> > Hi, >> > >> > I have a question regarding the map data structure. I'm trying to >> program a >> > Sieve of Eratosthenes using the algorithm at Wikipedia: >> > >> > Input: an integer n > 1 >> > >> > Let A be an array of bool values, indexed by integers 2 to n, >> > initially all set to true. >> > >> > for i = 2, 3, 4, ..., while i^2 ≤ n: >> > if A[i] is true: >> > for j = i^2, i^2 + i, i^2 + 2i, ..., while j ≤ n: >> > A[j] = false >> > >> > Now all i such that A[i] is true are prime. >> > >> > I'm having a problem creating the data structure A. >> > >> > What I want to do is create a map of integers from 2 to n all >> initialized to >> > true that I can then prune using the algorithm. >> > >> > Any ideas? >> >> Since the keys are consecutive integers, you might consider a vector >> of booleans: >> >> (def A (vec (repeat (inc n) true))) >> >> You can then use assoc to set any particular index to false: >> >> (assoc A 5 false) >> >> Differences using a vector instead of a hash-map: will stay in numeric >> order, doesn't allow arbitrary dissoc, nth and assoc may be faster, >> use less memory, (vector-of :bool) will definitely use less memory, >> and probably others. Depending on your goals, a vector may or may not >> be preferable to a hash-map. >> >> --Chouser >> >> -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
