Thursday, July 17, 2008

Rubik's cube simplest solution!

(Taken from http://peter.stillhq.com/jasmine/rubikscubesolution.html and http://www.tj9991.com/rubiksguide/)








Rubik's Cube Terminology

When describing the solution for the 2nd and 3rd layers, standard
cube notation will be used. Here's what you need to know to read it:









F = front faceB = back faceR = right faceL = left faceU = up faceD = down face

In addition to a letter, each move may be accompanied by an apostrophe or the number two:


  • A letter by itself means turn that face 90 degrees clockwise (eg. F).

  • A letter followed by an apostrophe means turn that face 90 degrees anti-clockwise (eg.
    F').

  • A letter followed by the number 2 means turn that face 180 degrees (direction is irrelevant), (eg.
    F2).




So R U' L2 is shorthand for "turn the right face 90 degrees clockwise, then turn the up face 90 degrees anti-clockwise, then turn the left face 180 degrees".
When thinking whether to turn clockwise/anti-clockwise, imagine that
you are looking directly at the particular face you are turning.



Rubik's Cube The First Layer











first layer corner: step 1

Step 1

The blue/red/white corner is sitting in the bottom layer (the blue part is facing the bottom so we can't see it in this picture). Turn the blue face 90 degrees anti-clockwise.

first layer corner: step 2

Step 2

Now your cube should look like this. Move the D face 90 degrees anti-clockwise to line up the blue/white edge with the blue/white/red corner.

first layer corner: step 3

Step 3

Now that the blue/white edge and the blue/white/red corner have been lined up, re-form the white cross by turning the blue face 90 degrees clockwise.

first layer corner: step 4

Step 4

Now the blue/white/red corner is in its correct place.



Here are some tips for inserting the top layer corners:

  • Start with a first layer corner that is sitting in the last layer.

  • If there are multiple first layer corners in the last
    layer (there usually will be), start with one that does not have the
    white part of the corner on the face opposite the white face. Or, if
    you were using a different colour for the cross ('colour X'), start
    with a corner that does not have the 'colour X' part of the corner on
    the face opposite the 'colour X' face.

  • When working with a first layer corner piece that is
    in the first layer (but in the wrong first layer corner position), you
    will need to get it out of the first layer into the last layer, then
    insert it into the correct first layer corner position. The same
    principle applies if a first layer corner piece is in the correct first
    layer corner position but needs to be flipped around. You need to get
    it out of the first layer (ie. into the last layer), and then re-insert
    it into the first layer the correct way around.






completed first layer

This is what the first layer should look like when finished.




Rubik's Cube The Middle Layer



The middle layer consists of one stage:


  1. Insert the 4 middle layer edges (each edge is inserted individually).


You only need to learn one algorithm (plus the mirror algorithm) for
the second layer. There are many more algs, but let's just learn the
essential one first.

First, locate a middle layer edge that is currently sitting in the last layer. I'm going to use the blue/red edge for this example.





This blue edge cubie in the last layer is the blue/red edge cubie.



In this picture, U=white, L=red and F=blue.
We can't see the other three faces, but obviously the R face is the one
opposite the L face, the D face is opposite the U face and the B face
is opposite the F face.

Now, position the blue/red edge piece so that the colour on the side of the cube (blue in this case) lines up with it's centre. Now perform the following algorithm: D L D' L' D' F' D F

If the blue/red edge piece was flipped the other way so that the blue was on the bottom rather than the red, you would position the cubie under the red centre and perform the following alg: D' F' D F D L D' L'.
This is the mirror of the previous algorithm. The axis of symmetry lies
diagonally across the white face, and along the line which divides the blue face and the red face.



Rubik's Cube The Last Layer



The last layer ("LL") is done in 4 steps:


  1. Orient the edges (2 algs) - i.e. form a cross on the D face.

  2. Permute
    the corners (1 alg) - i.e. get the corners in the correct position in
    3D space (don't worry if they still need to be rotated).

  3. Orient the corners (1 alg + mirror alg) - i.e. flip the corners.

  4. Permute the edges (1 alg) - i.e. swap the edges around. The cube should now be solved! :)



All last layer algorithms are performed with the cross (i.e. the first layer -
white side in this example) on the bottom.



Rubik's Cube Orienting the LL Edges


Once you have completed the first two layers ("F2L"), hold the cube
so that the white side is on the bottom. The white side will be on the
bottom for the remainder of the solution. This means that the white
side is the D side for all last layer algorithms.



On my cube, white is opposite yellow, therefore yellow is the U face
for all last layer algorithms on my cube. Note that your cube may have
a different colour opposite white (e.g. blue). Now have a look at your
last layer, and in particular, look at the last layer face - there are
4 possible patterns of LL edges that you may see.







State 1

State 2

State 3

State 4




Unlike with the initial cross (where all the edges must match up
with the white centre and with the centres on the middle layer), here
all you need to worry about is getting all the last layer edges
matching up with the last layer centre. It doesn't matter if the other
colour on the LL edge piece does not match up with the colour on the
middle layer centre. Also, ignore the LL corners too. It doesn't matter
what they are doing at the moment. Now, let's consider each of these LL
edge states separately.








State 1

All the edges are already oriented correctly. Move on to permuting the corners.









State 2

We are going to re-orient our faces for this
algorithm. The face you are looking directly at in this picture is now
the U face (it was the D face for when you were doing the second layer
edges). Perform the following algorithm: F U R U' R' F'









State 3

As with State 2, the face you are looking directly at in this picture is now the U face. Perform the following algorithm: F R U R' U' F'









State 4

State 4 is really a combination of States 2 and
3, so all you need to do is perform the algorithm for either State 2 or
State 3. Once you've done this, you'll see that your LL edges now look
like State 2 or State 3, so just perform the appropriate algorithm and
you will have a cross on the LL.






Orienting the LL Corners


There are 8 possible orientation states for the LL corners. One is
where all 4 corners are correctly oriented. The other 7 look like this.












State 1

State 2

State 3

State 4

State 5

State 6

State 7









State 1. Twisting three corners anti-clockwise

R' U' R U' R' U2 R U2









State 2. Twisting three corners clockwise

R U R' U R U2 R' U2


To see an animated version of this algorithm, look at
Lars Petrus' Sune algorithm.



States 3-7

Once you know the algorithms for
States 1 and 2, you can solve any LL orientation State. The remaining
States can be oriented using a maximum of 2 algorithms. You will need
to do one of the following (i) the State 1 algorithm twice, (ii) the
State 2 algorithm twice, (iii) the State 1 algorithm, then the State 2
algorithm, or (iv) the State 2 algorithm, then the State 1 algorithm.

In a previous edition of this solution, I had said that I'm not
going to tell you exactly how to combine the State 1 and State 2
algorithms to solve States 3-7. My reason for this was because it is
important that you try to understand how the State 1 and the State 2
algorithms work, and that once you do understand them you will be able
to work out how to use them to solve all the States. I still believe
this, however, I received emails from a few people who were having
trouble with States 3-7, so I decided to write some extra tips.


Permuting the LL Corners


The two possible states are:



  • two adjacent LL corners need to be swapped; or

  • two diagonal LL corners need to be swapped.


These are the only two possible states. If you cannot identify one of these two states with your LL corners then one
or more of the following must be true:



  • You have not finished the F2L.

  • Someone has ripped out a corner of your cube and put it in the wrong way.

  • Someone has ripped off some of your stickers and put them back in the
    wrong place.

  • You are not looking hard enough. ;)


Swapping adjacent corners


Hold the cube with the white side on the bottom, and the two
corners to be swapped are in the front right top and the back right top
positions. Perform the following algorithm: L U' R' U L' U' R U2.


Swapping diagonal corners


Swapping diagonal corners can be done by executing the adjacent
corner swap algorithm twice. Perform it once to swap any two LL
corners. Re-examine you cube and you'll see that now there are just two
LL corners that need to be swapped. Position it correctly for the final
LL adjacent corner swap and perform the LL adjacent corner swap
algorithm.




Permuting the Edges

The following are the two algorithms you need to know for moving three edges clockwise and counter clockwise.













     
(R2' U)(R U R' U')(R' U')(R' U R')       (R U')(R U)(R U)(R U')(R' U' R2)

 


Nutshell :


Step 1. Complete one side for any colour


Step 2. Go for te middle line colour allignment using D L D' L' D' F' D F
or D' F' D F D L D' L'

Step 3. Arrange the center pieces of the layer opposite the completed layer using F U R U' R' F' or F R U R' U' F'


Step 4. Arange the corners of this layer using R' U' R U' R' U2 R U2 or R U R' U R U2 R' U2


Step 5. If the corners in the last layer need to be aligned, use L U' R' U L' U' R U2


Step 6. Surely just the center pieces now need to be arranged in last layer using R2' U R U R' U' R' U' R' U R' or R U' R U R U R U' R' U' R2


(Taken from http://peter.stillhq.com/jasmine/rubikscubesolution.html and http://www.tj9991.com/rubiksguide/)

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