Tic-Tac-Toe

Tic-Tac-Toe, also called noughts and crosses, is the quick pencil-and-paper game almost everyone learns as a child. Two players take turns marking empty squares on a grid, one with X and one with O. Whoever gets their marks in an unbroken line first, across, down or corner to corner, wins. Here you can play the computer at three levels or pass the phone to a friend, and play single games or a best-of-three or best-of-five match.

How to play

• Tap an empty square to put your mark there. On a computer you can also use the arrow keys and Enter, or the keys 1 to 9 on the small board.
• On the classic 3 × 3 board you need three in a row. On the 5 × 5 and 7 × 7 boards you need four in a row.
• If the board fills up, or no line can be finished by anyone any more, the game is a draw.
• In a match, the two sides take turns starting. When a game ends, tap anywhere to start the next one.

Computer levels

Easy plays almost at random, which makes it a gentle first opponent. Medium always takes a win when it has one and blocks yours, but it can be caught by a fork. Hard plays perfectly on the 3 × 3 board, so the best you can do there is a draw. On the bigger boards Hard searches several moves ahead and is tough to beat, but it can be done.

Tips

• On 3 × 3, start in a corner. It gives your opponent the most chances to go wrong.
• Make a fork: a move that creates two lines that each need just one more mark. Your opponent can only block one of them.
• When your opponent takes a corner first, answer in the centre, or you may face a fork.
• On the bigger boards, watch for three marks in a row with empty squares at both ends. That threatens two wins at once, so stop a row of two before it grows.
• Play near the middle on the big boards. Central squares belong to more possible lines.