FYI, I tried re-writing count-terms using loop/recur, but it didn't
really make a difference:
(defn count-terms-recur [n]
(loop [n n
count 1]
(cond
(= 1 n) count
(even? n) (recur (/ n 2) (inc count))
:else (recur (inc (* n 3)) (inc count)))))
Clojure 1.2 = 1153.43 msecs
Clojure 1.3 Alpha 1 = 190769.86 msecs
On Sep 24, 10:41 am, Btsai <[email protected]> wrote:
> After updating from Clojure 1.2 to Clojure 1.3 Alpha 1, I noticed that
> one of my Project Euler solutions became dramatically slower. The
> solution was for Problem 14, finding the number less than N that
> produces the longest Collatz sequence.
>
> For N = 100,000, the time required to find the answer was as follows:
>
> Clojure 1.2 = 1327.45 msecs
> Clojure 1.3 Alpha 1 = 191186.76 msecs
>
> (For Problem 14, N is actually 1,000,000, but I ran out of patience
> waiting for the code to produce the answer in Clojure 1.3 Alpha 1)
>
> Has anyone run into something like this, or know what might have
> caused the dramatic difference in speed?
>
> The code:
>
> (defn next-term [n]
> (if (even? n) (/ n 2)
> (inc (* n 3))))
>
> (defn count-terms [n]
> (if (= 1 n) 1
> (inc (count-terms (next-term n)))))
>
> (let [pair (juxt identity count-terms)
> pairs (map pair (range 1 100000))]
> (println (first (apply max-key second pairs))))
>
> Machine specs:
>
> Intel Core 2 Duo T9300 @ 2.5 GHz
> 2 GB RAM
> JVM is running on server mode
>
> P.S. I originally wanted to write that last part of the code a little
> more elegantly, like this:
>
> (println (apply max-key count-terms (range 1 100000)))
>
> But that made things even slower:
>
> Clojure 1.2 = 2764.48 msecs
> Clojure 1.3 Alpha 1 = 740025.36 msecs
>
> I think I read somewhere that max-key applies f more times than is
> necessary, so should not be pass any f that takes significant time to
> compute.
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