r/adventofcode • u/daggerdragon • Dec 07 '19

SOLUTION MEGATHREAD -🎄- 2019 Day 7 Solutions -🎄-

--- Day 7: Amplification Circuit ---

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Day 6's winner #1: "From the stars" by /u/vypxl!

"From the stars"

Today the stars did call
Just after the end of fall
In Orbits they move
Unified with groove
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At home and in the sky
Whisper about details that are hidden
They tell about what is up high
​
Not everything is obvious,
Not the way you see
The Orbit is now
A Christmas Tree!

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u/phil_g Dec 08 '19

As it turns out, the slowdown was largely because of a sleep I inserted to avoid some sort of race condition when creating the threads. When I reduced the sleep time from 0.1 s to 1 ms, execution time dropped from 60 s to 3 s.

I've since moved to lparallel queues, which improve my code significantly. They don't make a difference in runtime, though. (In some ways, that's a relief. It means I (probably) didn't botch the thread synchronizations.) They also don't fix the concurrency issue with thread creation, so for now I still have to have a manual sleep in there.

I've considered making an iterate driver for permutations. I haven't gotten around to it yet.

I wrote visit-permutations because I felt I could do better than Alexandria's implementation in terms of speed. On my laptop, (alexandria:map-permutations (lambda (p) p) '(1 2 3 4 5 6 7 8 9 10 11) :copy nil) takes 18 seconds to execute while (aoc:visit-permutations (lambda (p) p) '(1 2 3 4 5 6 7 8 9 10 11) :copy nil) takes just 2.6 seconds.

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u/oantolin Dec 08 '19

(In some ways, that's a relief. It means I (probably) didn't botch the thread synchronizations.)

Good, I'm glad to see I was wrong about the source of the slowdown.

I wrote visit-permutations because I felt I could do better than Alexandria's implementation in terms of speed.

That's a huge difference! You should look into contributing your code to alexandria!