Imagine a 3x3x3 cube made of 27 little cubies. Imagine each of these cubies has a number 1 through 9 in it. No two cubies in a plane have the same number. A plane is a horizontal, vertical(left-right), or vertical(up-down) cross-section of 9 cubies.

You know the numbers in some of the cubies. What are the others?

Grid diagram

+ - + - + - +            3D diagram
|   | 5 | 1 |
+ - + - + - +              + - + - + - +
|   |   | 6 |             /   / 5 / 1 /|
+ - + - + - +            + - + - + - +1+
| 3 |   |   |           /   /   / 6 /|/|
+ - + - + - +          + - + - + - +6+ +
                      / 3 /   /   /|/|/|
+ - + - + - +        + - + - + - + + + +
|   |   |   |        | 3 |   |   |/|/|/
+ - + - + - +        + - + - + - + + +
|   | 8 |   |        | 2 | 6 |   |/|/
+ - + - + - +        + - + - + - + +
| 2 | 6 |   |        |   |   |   |/
+ - + - + - +        + - + - + - +

+ - + - + - +
|   | 7 |   |
+ - + - + - +
| 9 | 4 |   |
+ - + - + - +
|   |   |   |
+ - + - + - +

Note: The 1, 3, 5, and 6 are in the same horizontal plane. (top)
The 1 and 6 are in the same vertical(up-down) plane. (right-most)
The 2, 3, and 6 are in the same vertical(left-right) plane. (front)

(In reply to re: Did anyone notice... by Tristan)

Yes, after some experimentation, I found a simple strategy to "mix up" the squares.  I've also found that you can take any two parallel planes and switch them, and everything is still "legal".  If anyone is looking forward to Part II, you will not find a pattern.  Sorry :)

Posted by Dustin on 2006-03-08 10:26:10