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k

kef

12/10/2018, 12:05 AM
In the last AoC challenge you have to put marbles in a circle (linked list), sometimes moving back 7 places from the current position. Stripped version of the my code for that is below. I thought that the straight forward
current.prev.prev.prev.prev.prev.prev.prev
should be the fastest way possible, but out of curiosity I also did it as
generateSequence(current) { it.prev }.take(8).last()
and to my surprise, when I measured times of execution I got this : -
.prev
chain -> 2389ms -
generateSequence
-> 460ms So why is
generateSequence
5 times faster? On my machine I get results like that when looping up to 10mln, after that
generateSequence
suddenly takes 3s to finish.
t

todd.ginsberg

12/10/2018, 12:41 AM
If you are doing AoC, there are quite a few of us in #advent-of-code!
k

kef

12/10/2018, 12:51 AM
Thanks! Will link my question there 🙂
k

karelpeeters

12/10/2018, 1:38 AM
It appears to hit some worst-case scenario in the interpreter, but after a couple of iterations I get
60ms
for the sequence and
40ms
for the
.prev.prev
thing as expected.
👍 1
k

kef

12/10/2018, 10:24 AM
I know that after JIT kicks in times get better. But how can I verify it is the case and what exactly makes it hit the worse case scenario? Also, is there any way to improve it for a single run (like running it once as .kts)?
k

karelpeeters

12/10/2018, 11:40 AM
Maybe running it with native makes it better?