Wednesday, August 11, 2010

God's Number is 20

As many of my friends know, I am a competitive speedcuber (one can search up my WCA profile).

I love solving puzzles, and more importantly, I love the mathematics behind it. For some time now in the cubing world there has been some progress made into solving an algorithm which produces a solution having the least possible number of moves, the idea being that an omniscient being would know an optimal step from any given configuration. This is known as God's algorithm. The number of moves this algorithm would take in the worst case is called God's Number.

Recently
Morley Davidson, John Dethridge (also a TopCoder), Herbert Kociemba, and Tomas Rokicki proved that God's Number for the standard 3x3x3 Rubik's Cube is exactly 20.

Why is this a great leap forward for cubers? Simply put, imagine constructing an algorithm to optimally
solve all 43,252,003,274,489,856,000 positions of the cube. Easy, no? It took 3 decades to get to this stage ..

Here's the
article for further reading.

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