This project implements the classic Tic-Tac-Toe game using a simple, command
line interface. Compiling and running it should be possible on any standard
Un*x implementation that has a g++ compiler and STL available.

You do need to have cppunit installed, and LD_LIBRARY_PATH set to point
to where its so file lives.

=====================================

TTT Game Design

-> Numbering the game grid <-

 0 | 1 | 2
-----------
 7 | 8 | 3
-----------
 6 | 5 | 4

This allows even numbers to be at the corners, 
odd numbers on the sides and the middle square 
to be 8. This scheme makes the rules for choosing
a computer move much easier.

The grid presented to the user will be more straightforward:

 1 | 2 | 3
-----------
 4 | 5 | 6
-----------
 7 | 8 | 9

Note that the rest of the description of the game will be in
terms of the computer grid rather than that presented to the human.

-> Winning combinations <-

(0 1 2)
(0 4 8)
(0 6 7)
(1 5 8)
(2 3 4)
(2 6 8)
(3 7 8)
(4 5 6)

-> Blocking combinations <-

If these pairs are found in a set of moves, then picking the corresponding
square will produce a win. The computer will use this to either block a 
potential win by the human, or itself take the square to win the game.

(0 ((1 2) (6 7) (8 4)))
(1 ((5 8) (0 2)))
(2 ((0 1) (6 8) (3 4)))
(3 ((7 8) (2 4)))
(4 ((2 3) (0 8) (5 6)))
(5 ((1 8) (4 6)))
(6 ((4 5) (2 8) (0 7)))
(7 ((0 6) (3 8)))
(8 ((0 4) (1 5) (2 6) (3 7)))

-> Processing sequence after human makes a move <-

1) Check for valid human move. If not valid, prompt for
another move. Otherwise continue.

2) Add the human move and check whether the human has 
won. If so, announce the win and prompt for another game. 
Otherwise continue.

3) Check whether any squares are free after the 
human has moved. If not, declare a draw. Otherwise
continue.

4) Check whether the computer can move and win. If so,
make the move, announce the win and prompt for another
game. Otherwise continue.

5) Check whether the computer can block the human
from winning. If so, make the move and check whether
any other moves are available. If so, prompt for
another human move. If not, declare a draw.
Otherwise continue.

6) Find the best computer move. Make the move and
check whether another move is available. If not,
declare a draw and ask for another game. If so, prompt 
the human for another move.

-> Processing sequence for selecting a computer move <-

1) If only one square is free, pick it. Will have already
checked above whether this was a win for the computer, so
the game must be a draw. 

2) Else if the center square is not taken, take it.

3) Else if only the 8 square is taken (by the human), 
take an even (corner) square.

4) Else if computer has the center square and human has
one other square, move in square ((human + 3) mod 8).

This covers both odd and even cases. If the human has
selected an odd square, in this case 1, the computer
will move to 4 and win:

   | X |
-----------
   | O | 
-----------
   |   | O

If the human has taken an even square, in this case
0, the computer will move to 3 and force a draw. Note that
no other rules are needed to complete the draw. The human's
block of the computer winning will force the computer
to block the human from winning, which will continue to
a draw unless the human fails to block.

 X |   |
----------
   | O | O
-----------
   |   | 


5) Else if the computer has the 8 square and human
has two even squares, move to an odd square.

This covers the case:

 X |   |
-----------
   | O | 
-----------
   |   | X

If the computer picks a corner square, the human will
pick the other corner square and win.

6) Else if the computer has the 8 square, the human
has an odd and an even square:

if odd == ((even + 3) mod 8) then move ((odd + 2) mod 8)
if odd == ((even + 5) mod 8) then move ((even + 3) mod 8)

This is a hard case. It could be either

 X |   |
-----------
   | O | 
-----------
   | X | 

or

 X |   |
-----------
   | O | X
-----------
   |   | 

If the computer picks wrong, the human will pick the 
corner between the two previous moves and win. Going
to the even move plus two forces the human to block
and will result in a draw.

7) If the computer has an even square, and the human has
an even square and the 8 square, pick another corner square.

 X |   |
-----------
   | X | 
-----------
   |   | O

If the computer picks an odd square, the human can take a corner 
square and win.  

8) Else if the computer has 8 and human has two odd, 
pick the even square one greater than the greatest odd. If 
the human is able to pick the square between its previous
moves, the human will win.

   | X |
-----------
   | O | X
-----------
   |   | 

As long as the human blocks correctly, the game will end
in a draw. This also covers the following case:

   |   |
-----------
 X | O | X
-----------
   |   | 


9) Else if there is more than one square open, take any of them.

This covers the cases like:

 X |   |
-----------
 O | O | X
-----------
 X |   | 

   | X | O
-----------
   | O | X
-----------
 X |   |