kociemba

This Python package contains two equivalent implementations (in C and Python) of Herbert Kociemba's two-phase algorithm for solving Rubik's Cube. Original Java implementation can be found here: http://kociemba.org/download.htm.

These ports are pretty straightforward (not to say dumb) and most probably can be optimized. But they have been extensively tested in our Rubik's cube solving machines (FAC System Solver and Meccano Rubik's Shrine), so be confident the algorithm is working.

NB please note that two-phase algorithm does not guarantee that the produced solution is the shortest possible. Instead, it gives you a "good enough" solution in a very short time. You can implement additional checks on top of this library, for example, to not produce any moves if the cube is already solved.

Installation

This package is published on PyPI and can be installed with:

$ pip install kociemba

It was tested under Python 2.7 and 3.3+.

Unix-based systems

You might need to install libffi system library beforehand. For example, on Debian-based distributions (e.g. Raspbian) you would run sudo apt-get install libffi-dev.

Windows

Library should work on Windows, however it is not automatically tested at this moment: Travis CI doesn't have windows support.

Normal pip install kociemba (or pip3 install kociemba for Python 3.3+) should work, but you will need to install free build tools from Microsoft first. Check the following links:

• for Python 2.7: https://www.microsoft.com/en-us/download/details.aspx?id=44266
• for Python 3: https://www.visualstudio.com/downloads/#build-tools-for-visual-studio-2017

Usage

The package exposes just one function solve(), which accepts a cube definition string and returns a solution string in standard notation (see below). Optional second argument allows solving to a specific pattern.

>>> import kociemba

>>> kociemba.solve('DRLUUBFBRBLURRLRUBLRDDFDLFUFUFFDBRDUBRUFLLFDDBFLUBLRBD')
u"D2 R' D' F2 B D R2 D2 R' F2 D' F2 U' B2 L2 U2 D R2 U"

>>> kociemba.solve('FLBUULFFLFDURRDBUBUUDDFFBRDDBLRDRFLLRLRULFUDRRBDBBBUFL', 'BBURUDBFUFFFRRFUUFLULUFUDLRRDBBDBDBLUDDFLLRRBRLLLBRDDF')
u"R' D2 R' U2 R F2 D B2 U' R F' U R2 D L2 D' B2 R2 B2 U' B2"

Standalone tool

When installing with pip, kociemba will also register a command line tool with the same name. So you can also use it like this:

$ kociemba <cubestring>

Cube string notation

The names of the facelet positions of the cube (letters stand for Up, Left, Front, Right, Back, and Down):

             |************|
             |*U1**U2**U3*|
             |************|
             |*U4**U5**U6*|
             |************|
             |*U7**U8**U9*|
             |************|
 ************|************|************|************
 *L1**L2**L3*|*F1**F2**F3*|*R1**R2**R3*|*B1**B2**B3*
 ************|************|************|************
 *L4**L5**L6*|*F4**F5**F6*|*R4**R5**R6*|*B4**B5**B6*
 ************|************|************|************
 *L7**L8**L9*|*F7**F8**F9*|*R7**R8**R9*|*B7**B8**B9*
 ************|************|************|************
             |************|
             |*D1**D2**D3*|
             |************|
             |*D4**D5**D6*|
             |************|
             |*D7**D8**D9*|
             |************|

A cube definition string "UBL..." means that in position U1 we have the U-color, in position U2 we have the B-color, in position U3 we have the L color etc. according to the order U1, U2, U3, U4, U5, U6, U7, U8, U9, R1, R2, R3, R4, R5, R6, R7, R8, R9, F1, F2, F3, F4, F5, F6, F7, F8, F9, D1, D2, D3, D4, D5, D6, D7, D8, D9, L1, L2, L3, L4, L5, L6, L7, L8, L9, B1, B2, B3, B4, B5, B6, B7, B8, B9.

So, for example, a definition of a solved cube would be UUUUUUUUURRRRRRRRRFFFFFFFFFDDDDDDDDDLLLLLLLLLBBBBBBBBB

Solution string consists of space-separated parts, each of them represents a single move:

• A single letter by itself means to turn that face clockwise 90 degrees.
• A letter followed by an apostrophe means to turn that face counterclockwise 90 degrees.
• A letter with the number 2 after it means to turn that face 180 degrees.

e.g. R U R’ U R U2 R’ U

C version

C sources reside in the ckociemba folder. Running make inside this directory will compile a standalone binary. It accepts a cube representation as a command line argument, and writes the solution to the standard output. You can, of course, use ckociemba sources directly in your projects.

Performance

When possible, kociemba will use C implementation under the hood. If something goes wrong (C version cannot be imported) it will automatically fall back to pure-Python implementation. However, it will be much slower.

Testing

To run the tests, clone the repository and run:

$ python setup.py test

Thanks to

• @jarheadjoe for his contribution to Windows support