Because of the simplicity of tic-tac-toe, it's often used as a pedagogical tool for teaching the concepts of excellent sportsmanship and therefore the branch of AI that deals with the searching of game trees. it's straightforward to write down a computer virus to play tic-tac-toe perfectly, to enumerate the 765 essentially different positions (the state space complexity), or the 26,830 possible games up to rotations and reflections (the game tree complexity) on this space.

The game are often generalized to an m,n,k-game during which two players alternate placing stones of their own color on an m×n board, with the goal of getting k of their own color a row. Tic-tac-toe is that the (3,3,3)-game. Harary's generalized tic-tac-toe is a good broader generalization of tic tac toe. It also can be generalized as a nd game. Tic-tac-toe is that the game where n equals 3 and d equals 2. If played properly, the sport will end during a draw making tic-tac-toe a futile game.

Courtesy : https://en.wikipedia.org/wiki/Tic-tac-toe