On 05/08/2022 23:02, wij wrote:
> Is there any program that solves scrambled Rubik cube in 20 moves?
The reference I gave a few days ago, "http://www.cube20.org
has a link to their source. I don't know whether this is what you
> From what I searched on the internet, the answer is probably NO.
> Then, from the example https://rubiks-cube-solver.com/solution.php?cube=0111111113222222222334333334144444644555555555663666666
> the Rubik cube remaining only 2 mismatched corners may still need 17 moves
> to finish, this suggests to me all other strategies commonly seen on the
> internet (e.g. layer by layer, cross centers first,...) are not much different
> from any chosen random cubes that are ~3 steps closer to the goal.
> Is my understanding of the Rubik cube problem right?
Probably not. Solving layer by layer, etc., is certainly far
from optimal, witness the much larger upper bounds given by the early
solvers [such as Singmaster, Conway, Thistlethwaite]. Note that ~98%
of all positions are >= 17 moves from solution; it wouldn't be at all
surprising if some of them are visually quite nearly solved. In the
days when I was interested in this sort of problem in relation to
sliding-block puzzles [see
(includes source, of a sort); very old] and chess endgame databases,
there were always "surprises" where problems turned out to have very
long or very short solutions.
Andy Walker, Nottingham.
Andy's music pages: www.cuboid.me.uk/andy/Music
Composer of the day: www.cuboid.me.uk/andy/Music/Composers/Hertel