What you need to know.

# What you need to know.

The Rubik's Cube is a 3-D mechanical puzzle invented in 1974 by Hungarian sculptor and professor of architecture Erno Rubik. In a classic Rubik's Cube, each of the six faces is covered by nine stickers, among six solid colours (traditionally white, red, blue, orange, green, and yellow). A pivot mechanism enables each face to turn independently, thus mixing up the colours. For the puzzle to be solved, each face must be a solid colour.

### Number of possible positions.

The Cube has eight corners and twelve edges. There are 8! (40,320) ways to arrange the corner cubes. Seven can be oriented independently, and the orientation of the eighth depends on the preceding seven, giving 3^7 (2,187) possibilities. There are 12!/2 (239,500,800) ways to arrange the edges, since an odd permutation of the corners implies an odd permutation of the edges as well. Eleven edges can be flipped independently, with the flip of the twelfth depending on the preceding ones, giving 2^11 (2,048) possibilities. In total, there are exactly 43,252,003,274,489,856,000 permutations, which is approximately forty-three quintillion. The puzzle is often advertised as having only "billions" of positions, as the larger numbers are unfamiliar to many. To put this into perspective, if one had as many 57-millimeter Rubik's Cubes as there are permutations, one could cover the Earth's surface with a layer 275 cubes thick.

### Move notation.

All Rubik's Cube enthusiasts use a notation developed by David Singmaster to denote a sequence of moves, referred to as 'Singmaster notation'. Its relative nature allows algorithms to be written in such a way that they can be applied regardless of which side is designated the top or how the colours are organised on a particular cube.

* F (Front): the side currently facing you

* B (Back): the side opposite the front

* U (Up): the side above or on top of the front side

* D (Down): the side opposite the top, underneath the Cube

* L (Left): the side directly to the left of the front

* R (Right): the side directly to the right of the front

When a prime symbol ( ' ) follows a letter, it denotes a face turn counter-clockwise, while a letter without a prime symbol denotes a clockwise turn. A letter followed by a 2 (occasionally a superscript 2) denotes two turns, or a 180-degree turn. For instance, R is right side clockwise, but R' is right side counter-clockwise. A move sequence is denoted consecutively, like RFB'U2R'.