Slashdot Mirror

← Back to Stories (view on slashdot.org)

Rubik's Cube Now Solvable in 20 Moves

Posted by CmdrTaco on from the good-use-of-spare-time dept.

A few years ago we reported that it had been proven that Rubik's Cubes could be solved in 23 moves. Well now that number is down to just 20. Proving it required 35 years of computer time donated by Google to get it done.

9 of 309 comments (clear)

  1. There is a good reason by calderra · · Score: 5, Interesting

    I know it won't stem the tide, but this is good research. I'm sure there are a million other algorithms in the world that can benefit from this. Shortcuts they had to invent to make sure they were using minimal processing time, full understanding of how much money and time it really took to get this process done to make other projects more practical, etc etc. This sort of thinking, even if silly on its own, has a broad range of applications.

  2. Re:Thank God! by kg8484 · · Score: 2, Interesting

    If you've got a computational problem that would help towards a cancer cure, have you asked Google to donate time for it?

    No, he'd rather just complain. It's much easier to criticize researchers than to do the research yourself.

  3. They're counting double moves as one by BitterKraut · · Score: 2, Interesting

    I wouldn't say they're cheating, but I am a bit dissatisfied with their way of counting moves. Rotating a face by 180 degrees is not an elementary move to me. I'd like to know god's number in elementary moves.

    1. Re:They're counting double moves as one by allusionist · · Score: 1, Interesting

      It's a bit subjective, honestly. I count 18 elementary moves - each of the 6 faces rotated in one of three ways - quarter clockwise, quarter counterclockwise, or half. Some people also consider slices (rotating the center but not the sides) an elementary move, giving 6 more elementary moves (each of the two slices rotated 3 ways) - I consider them two opposing edge rotations, just as you consider a half rotation two quarter rotations. In the end, however, all that matters is consistency - if you can solve a configuration in 10 moves (counting a single half-turn as two moves) and I say I can solve it in 9 (by counting it differently) that's when we have a problem. But in a case like this, since they are already setting an arbitrary target number of moves, it doesn't matter how they count them /so long as the results are compared to other results counted in the same way/.

  4. Re:Enough! by clone53421 · · Score: 2, Interesting

    Unzipping a fly with one hand is a bit like tying shoes.

    You’re an expert at tying shoes? Now go try tying someone else’s shoes.

    --
    Alexander Peter Kristopeit bought his basement from his mommy for one dollar.
  5. Re:Enough! by Ngarrang · · Score: 3, Interesting

    More and more women are going braless, or are wearing a sports bra. Gone are the days of the hooks.

    --
    Bearded Dragon
  6. Re:Thank God! by Entropius · · Score: 3, Interesting

    There's a movement in health research now geared at extending what they call "healthspan" rather than just "lifespan" -- not "how long does this dude keep breathing", but "how long can we keep this dude active and happy"?

    Turns out that many of the things that make people live longer also make their late years healthier. My grandfather is 94 and still travels the world with his girlfriend (a spry young 75, but he'll never see her again now that she's taken up Farmville). He got prostate cancer a few years ago (and colon cancer a few decades ago), received aggressive treatment for it, and is now cancer-free and healthy.

    Old does not *have* to mean feeble. Sometimes it does, of course, and that's bad; this is why we should look at healthspan rather than lifespan.

  7. Re:Thank God! by Alyred · · Score: 2, Interesting

    Indeed... once you pop one of the corners out with a flathead screwdriver, the rest come out pretty easily. The bad part is that after a few times doing this, the plastic becomes a bit worn and the edges won't hold the cubes in as well. It becomes patently obvious that the cube has been disassembled; a few more times and the cube starts to fall apart when turned and twisted normally. Or maybe I just got cheap models as a kid.

  8. Re:Thank God! by Anonymous Coward · · Score: 1, Interesting

    I can’t comment but on two of those, first being the moon landing photos, which were of course not faked (and much evidence exists to support this).

    Secondly, the fluoridation of water... if you look into the studies which were done to determine whether the effect of fluoride on teeth has any correlation to the occurrence of dental caries (tooth decay), you will find that (as any good researchers should) the researchers used a control group: the cavity rate amongst children in a number of cities in which the water was not fluoridated was also recorded. The result of the study? As predicted, the cavity rate declined in the cities where the water supply was fluoridated. And the cavity rate declined by a statistically identical amount in the cities where the water supply was not fluoridated. Conclusion: Fluoride prevents cavities. Wait, what?

    P.S. As I work in the drinking water industry, I happen to know that fluoride is indeed a highly toxic waste, but dilution is the solution. That, and human bodies make really good filters.