井字棋

Tic-Tac-Toe (also called Noughts and Crosses or X's and O's) is a simple paper-and-pencil game for two players. Despite being trivial to master, it remains popular as a teaching tool and children's game.

Get three of your marks (X or O) in a horizontal, vertical, or diagonal row.

Draw a 3x3 grid. One player uses X, the other uses O. X traditionally goes first.

1. Players take turns placing their mark (X or O) in an empty cell.
2. Once placed, marks cannot be moved or removed.
3. The first player to get three marks in a row wins.
4. Rows can be horizontal, vertical, or diagonal (8 possible winning lines).
5. If all nine cells are filled with no winner, the game is a draw (cat's game).

Win by placing three of your marks in any straight line (row, column, or diagonal). The game draws if all cells fill without a winner.

• *If you go first (X), play in a corner - it gives the most winning opportunities.
• *If opponent starts in the center, play a corner to maximize your chances.
• *If opponent starts in a corner, play the center.
• *Always block when your opponent has two in a row (unless you can win).
• *Create a 'fork' (two ways to win) when possible - opponent can only block one.
• *With perfect play from both sides, the game always ends in a draw.

Tic-Tac-Toe dates back to ancient Egypt. Similar games were played in Rome (Terni Lapilli) and medieval Europe. It's been 'solved' - perfect play always leads to a draw.