Hi there,
I had a look at the implementations of Knuth's algorithm S at rosetta
code: http://rosettacode.org/wiki/Knuth's_algorithm_S#Racket
What baffles me is the fact that the Racket version is so slow. Running
some sample on my laptop I have:
Ruby: ruby kas.rb 0.57s user 0.01s system 99% cpu 0.574 total
Perl: perl kas.pl 1.24s user 0.00s system 99% cpu 1.244 total
Racket: racket kas.rkt 2.68s user 0.01s system 99% cpu 2.700 total
I tried to improve but didn't get a significant improvement.
Finally, I found why it is slow. In the Racket sample there is:
(when (< (random) (/ n count))
(vector-set! vec (random n) item))
which I changed to
(when (< (* count (random)) n)
(vector-set! vec (random n) item))
Now I have:
racket kasX.rkt 0.36s user 0.01s system 99% cpu 0.372 total
This far slower than compiled languages but I think it
is quite ok.
The slowness seems to have to do with rational and converting from
rational to real, just my guess.
Question: Is the way I improved it the right way, or is there a better
more idiomatic approach?
--
Manfred
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