Hi Marek, I too am a mostly Python guy looking at clojure. I think you will like the for macro as it is a lot like list comprehensions. I did Euler45 in clojure too and https://github.com/thattommyhall/Project-Euler/blob/master/45.clj runs in 700ms I thought it was quite a nice soln: triangles, hexagonals and pentagonals is basically a transcription of the problem like yours and i decided to work on the vector [triangles pentagonals hexagonals] incrementing the ones with the smallest first element and filtering unless the 3 matched. I think there is a speedup as I peek at the first in each list twice but decided <1s was acceptable.
Tom 2011/1/20 Marek Stępniowski <mstepniow...@gmail.com>: > Hi, > I'm Marek Stępniowski, a Python developer trying to learn a new > language by night. I'm new to this group. > > When solving problem 45 from Project Euler [1] I have tried to learn > how lazy-seq macro should be used and wrote the code below:: > > (defn pentagonal-numbers [] > (map #(* 1/2 % (dec (* 3 %))) (iterate inc 1))) > > (defn hexagonal-numbers [] > (map #(* % (dec (* 2 %))) (iterate inc 1))) > > (defn equal-values [seqs] > "Given a list of ascending sequences, returns a lazy sequence containing > only values that exist in all of the sequences." > (if (empty? (first seqs)) > [] > (let [first-values (map first seqs)] > (if (apply = first-values) > (lazy-seq (cons (first first-values) > (equal-values (map rest seqs)))) > (let [min-value (apply min first-values)] > (recur (map #(if (= (first %) min-value) (rest %) %) seqs))))))) > > Unfortunately running:: > > (take 3 (equal-values [(pentagonal-numbers) (hexagonal-numbers)])) > > Results in heap space overflow exception (at max heap size = 256MB). > > I agree that it's a very naive solution, and that finding a third > element of the list will take a lot of time. I still fail to > understand why it's also needing all the memory. I'd be grateful for > any pointers. What am I doing wrong here? > > > [1] Project Euler problem 45: > http://projecteuler.net/index.php?section=problems&id=45 - I find > solving Project Euler problems is a good way to learn the new > language, while refreshing computer science and math theory at the > same time. If you're interested, you can find my git repository with > 39 problems solved here: https://github.com/zuber/project-euler > > > Thanks, > -- > Marek Stępniowski > http://stepniowski.com > > -- > 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
