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by mrandish 1426 days ago
I'm no expert but I took my kid to a speed-cubing event and we watched. The referees secretly set up the hidden cubes to be used for competition to specific randomized configurations which are determined automatically by a software program for each cube. I assume this program ensures that no competition cubes are scrambled such that they are excessively easy to solve.
1 comments
muti 1426 days ago
Interestingly, the rules only stipulate a minimum of two moves to solve. The implementation details of the official scrambling program may be stricter though

https://www.worldcubeassociation.org/regulations/#4b3

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nsilvestri 1426 days ago
The scrambling program tnoodle is open source and you can check out the implementation. [0]

I haven't verified myself, but I do think there is checking involved for some of the events (at least 3x3, 2x2, skewb, square-1, and pyraminx) to make sure the puzzles hit the minimum move limit. Other events like 5x5+ just use a sufficient number of random moves, because it would take too long to find and verify optimal solutions.

I can say in practice that the 2 move limit for 3x3 isn't a problem. I work on some personal projects related to cubing and was exploring the database [1] which has many historical scrambles. The shortest scramble ever generated was 12 moves long [2], and, from what I could tell from an extended inspection, is only "kind of" lucky. It's possible that some other simpler solves exist in the database but I haven't set my computer to crunch out the optimal solutions just yet.

I'm not particularly worried about really-short scrambles being randomly generated; my back of the envelope calculations suggest 3x3 scrambles of 8 moves or less as being one in 3.6 billion, while ~310,000 have been generated since 2014 and I estimate a seventh of them are never used (extra scrambles generated for a round if something goes wrong like the timer malfunctioning, the judge not following protocol, etc.).

[0] https://github.com/thewca/tnoodle

[1] https://www.worldcubeassociation.org/results/misc/export.htm...

[2] https://www.worldcubeassociation.org/competitions/SofiaAutum...

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