Tic Tac Toe

Tic Tac Toe is a paper-and-pencil game for two players.

Because of the simplicity of Tic TacToe, it is often used as a pedagogical tool for teaching the concepts of good sportsmanship and the branch of artificial intelligence that deals with the searching of game trees.

It is straightforward to write a computer program 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.

An early variant of Tic Tac Toe was played in the Roman Empire, around the first century BC.