as long as (reversible? of-whatever-collection) is true , last is almost a constant time operation
On Fri, Jun 10, 2011 at 8:20 AM, clojurefanxx <neuzhou...@gmail.com> wrote: > i'm a newbie working thru 4clojure.com's problems #19 thru #21 where > i'm asked to write a function, which when given a list or vector, > returns the last, penultimate, or an arbitrary nth element, > respectively. > > for problem #19 (return last element), using the function last was not > accepted as a good solution for both lists and vectors, but the > following was accepted: > > user=> (#(nth % (- (count %) 1)) '(5 4 3)) > 3 > user=> (#(nth % (- (count %) 1)) '[1 2 3 4 5]) > 5 > > for problem #21, (return arbitrary element) , using the function nth > or get was not accepted. > > --------------------------------------------------------------------------------------------- > Write a function which returns the Nth element from a sequence. > > (= (__ '(4 5 6 7) 2) 6) > > (= (__ [:a :b :c] 0) :a) > > (= (__ [1 2 3 4] 1) 2) > > (= (__ '([1 2] [3 4] [5 6]) 2) [5 6]) > > ------------------------------------------------------------------------------------------------ > > > i think using the nth or get functions on vectors to return an element > at index position n should be fine performance-wise, > but what's a general solution for lists that will perform better than > O(n)? (i 'm assuming that's the reason why > last, nth, and get were rejected when I tried them out as candidate > solutions??) > > thanks for any help! > > > > -- > 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 -- 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
