Ultimate Tic-Tac-Toe

Ultimate Tic-Tac-Toe turns the simplest game into a real strategy challenge. The big board is made of nine small tic-tac-toe boards. Win a small board with three in a row; win the game with three small boards in a row. The twist: the square you pick inside a small board sends your opponent to the matching small board. If that board is already finished, they may play anywhere.

The computer searches ahead with minimax and alpha-beta pruning — one move on Easy (with deliberate random moves) up to five moves on Expert.

1. You are ✕ and move first, anywhere on the board.
2. Your square's position (top-left, centre…) decides the small board the computer plays in next — and vice versa.
3. Win small boards with three in a row; win three small boards in a row to win the game.
4. The highlighted board shows where you must play.

• Think about where you send your opponent, not just where you play.
• Don't send them to a board where they can win — or to a free choice if you can avoid it.
• The centre board is the most valuable, as in normal tic-tac-toe.