I new the palindrome? function wasn't good in performance, but I didn't think it would be that bad. The type hinting does improve performance plus a mid way to compare. Thanks for pointing that out and the max-key function.
On Oct 12, 4:15 pm, Justin Kramer <jkkra...@gmail.com> wrote: > The 'palindrome?' function can be made much faster. Your version -- > which is idiomatic and fine when perf isn't a factor -- turns the test > string into a sequence, reverses it, turns it back into a string, then > checks for full equality with the original. There are faster (if > uglier) ways to check for palindromes. This version finds the Level 1 > answer in about 150ms on my machine: > > (defn palindrome? > [^String s] > (let [len (.length s) > mid (quot len 2)] > (loop [i 0 > j (dec len)] > (if (= i mid) > true > (when (= (.charAt s i) (.charAt s j)) > (recur (inc i) (dec j))))))) > > Also, the built-in function max-key will do what your sort/max-comp > code is doing more concisely: > > (apply max-key count (filter palindrome? (all-combs input))) > > HTH, > > Justin > > On Oct 12, 3:02 pm, tonyl <celtich...@gmail.com> wrote: > > > > > Hi, I just started to learn clojure in a more serious way and I am > > doing the first level of the greplin challenge. > > > I made it to work with a short palindrome like the example they give > > me, but when it comes to work with the input file, it takes for ever > > and I have to stop it. > > > $ time clj level1.clj > > ^C > > real 11m35.477s > > user 1m44.431s > > sys 9m3.878s > > > This is my code: > > > (defn palindrome? [s] > > (= s (reduce str (reverse s)))) > > > (defn all-combs [in] > > (let [len (count in)] > > (for [i (range 0 (- len 2)), j (range (+ i 1) len)] > > (subs in i j)))) > > > (defn max-comp [x y] > > (let [lenx (count x), leny (count y)] > > (cond (< lenx leny) 1 > > (= lenx leny) 0 > > (> lenx leny) -1))) > > > ;;(let [input "I like racecars that go fast"] > > (let [input (slurp "../_input/level1.in")] > > (println (nth (sort max-comp (filter palindrome? (all-combs > > input))) 0))) > > > The input file is thishttp://challenge.greplin.com/static/gettysburg.txt > > > It looks a bit procedural. It is long, but I don't think is the > > biggest bottleneck, I think it is my approach to create all the > > combinations possible for substrings. Maybe I should be using a lazy > > seq? How would I go to do that? -- 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
