Journal de bord

lundi 9 août 2010

God’s Number is 20

Every position of Rubik’s Cube™ can be solved in twenty moves or less.

With about 35 CPU-years of idle computer time donated by Google, a team of researchers has essentially solved every position of the Rubik’s Cube™, and shown that no position requires more than twenty moves.

Every solver of the Cube uses an algorithm, which is a sequence of steps for solving the Cube. One algorithm might use a sequence of moves to solve the top face, then another sequence of moves to position the middle edges, and so on. There are many different algorithms, varying in complexity and number of moves required, but those that can be memorized by a mortal typically require more than forty moves.

One may suppose God would use a much more efficient algorithm, one that always uses the shortest sequence of moves; this is known as God’s Algorithm. The number of moves this algorithm would take in the worst case is called God’s Number. At long last, God’s Number has been shown to be 20.

It took fifteen years after the introduction of the Cube to find the first position that provably requires twenty moves to solve; it is appropriate that fifteen years after that, we prove that twenty moves suffice for all positions.

God’s Number is 20”.

1. Le 9 août 2010,

Ah merde, c’était pas 42 ?

2. Le 10 août 2010,

42 ? Ha ! N00b !

3. Le 10 août 2010,

En tant que theoricien, j’attendais une jolie preuve avec tout plein de theorie des groupes, diagonalisation de matrices, etude des irreps, etc. Brute force, c’est laid.

4. Le 10 août 2010,
Laurent Gloaguen

Toujours quelqu’un pour cracher dans la soupe…

5. Le 10 août 2010,
Karl, La Grange
6. Le 12 août 2010,
Bob Marcel

ouais la force brute manque d’élégance, ce n’est pas très constructif.

Blah ? Touitter !