Tic-Tac-Toe

Tic Tac Toe - known here in the UK as Noughts and Crosses or Xs and Os - is one of the first "real" games most children learn. The rules are extremely simple and a game only lasts a few minutes. It also has the advantage that you don't have to buy any special equipment - you can play anywhere as long as you have paper and pencil to hand. Great for keeping the kids occupied!

Of course you can buy software to play the game or even play online should you wish. This is perhaps more useful in the case of the 3-d version of the game.

How To Play

To play Tic Tac Toe, simply draw a 3x3 grid - essentially the "hash" symbol on a phone. One player is "X" the other "O". Each takes it in turn to draw their symbol in an unoccupied square. The first player to make a row of three of their symbol - horizontally, vertically or diagonally - wins. If there is no winner when the board is full then the game is a draw.

Tic-Tac-Toe is a simple game with no luck. It is also very easy to analyse. With correct play the first player will never lose and can always win or draw. If the second player also plays correctly then the game will always be a draw. For this reason the appeal of the game wears off quickly once the winning strategy has been determined.

The ease with which the game can be analysed has made it a popular target for computer programmers and it is often used as a student project. It is easy to write a program that will play perfectly - a few simple rules will do the trick. A more interesting project is to write a program that learns how to win from its mistakes.

Variants

Many games - commercial and otherwise - are clearly based on Tic-Tac-Toe. One of the most popular and well known of these is Three Dimensional Tic Tac Toe - 3D OXO. This is played on a 4x4x4 board and the winner is the first to achieve a row of four pieces in any direction. This game is far more difficult and represents a challenge for most adults.

Note that the for the 3d game the board is four squares on each side, not three. On a 3x3x3 board the first player has a trivial guaranteed win.

The game can in theory be played in even more than three dimensions. In general for a game in n dimensions the board must be at least n+1 squares per side to avoid a trivial first player win.