The above write-up, and the one in
"
How to always win at 3D tic-tac-toe"
are true
only for a
3x3x3 grid.
Nontrivial (and
fun!)
3D tic-tac-toe
should be played on a
4x4x4 grid.
Of course, then the
objective is to get
four
in a row.
It is simple to draw the board on a piece of paper,
but takes
a bit of time to learn to
see the
board in
three dimensions. In
high school I spent
many hours of
lunch periods (and
history) playing this.
Below I sketch the board with one of the more difficult
to see
winning positions. (This wasn't a real game, which would have
gone on longer.)
You should think of the first board
as the top board, and the last as the bottom. See if you
can find the winning four in a row. There is a hint at the
bottom.
-----------------
| X | | | |
-----------------
| | | | |
-----------------
| | | O | |
-----------------
| | | | X |
-----------------
-----------------
| O | | | |
-----------------
| | O | | |
-----------------
| | | X | |
-----------------
| | | | |
-----------------
-----------------
| | | | |
-----------------
| | X | | |
-----------------
| | | | |
-----------------
| | | | |
-----------------
-----------------
| X | | | |
-----------------
| | O | | |
-----------------
| | | | |
-----------------
| | | | |
-----------------
Hint: X has won.