Plain tic-tac-toe is a draw once both players know it. Nesting nine boards inside a big one changes that, because of one rule. The cell you play decides which board your opponent plays in next. Every move is two moves at once. It's a mark on a small board, and it's an order you give your opponent about where to go. Most games are won and lost on that second part.
You play X and move first. The computer plays O.
Think about where you send them
Before placing a mark, look at the board your move would send the computer to. Ask three questions.
- Can O win that board right away? If O has two in a row there with the third cell open, don't send it there unless you have no choice.
- Is that board finished? Sending O to a won or full board gives it a free move anywhere. That's usually a gift.
- Where will O's reply send me? Each cell O might play sends you somewhere. If most of them send you to boards where you're weak, think again.
A useful habit is to judge each small board by who it's good for. A board where you have two in a row is a board you want to be sent to. So it's also a board where O will try not to send you.
Strategy that works
- Value the centre, but not blindly. The centre board takes part in four lines on the big board, more than any other. The centre cell of each small board also counts for a lot. But every centre cell you play sends O to the centre board. Overusing it gives O a lot of centre moves too.
- Win boards that make lines. A small board is only worth as much as the big-board lines it helps. Winning a corner board that sits on two of your open lines beats winning an edge board that O has already cut off.
- Sacrifice small boards. Sometimes the right move hands O a small board it can win, because the cell you play sends O somewhere useless. That's fine if that board doesn't help O on the big board.
- Use drawn boards as walls. A small board that fills with no winner counts for no one and blocks every big-board line through it. If O is building a big-board line, a drawn board in the middle of it ends that line.
A short worked example
Say you've won the top-left board and the centre board. The bottom-right board would complete your diagonal. O is watching it. Don't play into the bottom-right board yet. Instead, choose moves that send O to finished boards as rarely as you can. Steer O toward a board where its only safe replies send you to the bottom-right. Each cell in a small board points to one board, so you can often find a move where most of O's choices point back to where you want to be. When O runs out of safe cells, you get sent to the bottom-right with a two in a row waiting.
Mistakes to avoid
- Chasing one small board. Winning a board is good. Winning it by sending O to a board where it then wins is a trade, not a gain.
- Giving away free moves. Every time you send O to a finished board, it chooses where to play. Count how many finished boards your move points at.
- Forgetting the big board. Before celebrating a small win, check that the board sits on a line you can still complete.
Practising across the levels
Easy plays quick, beatable moves and only grabs obvious wins. It's the place to learn the sending rule until you check it without thinking. Medium searches several moves ahead but still makes mistakes fairly often. You'll need to avoid handing it easy boards and free moves to win. Hard reads deeper and slips much less, so beating it takes steady control of where it plays. Your record is kept for each level. A win on Hard usually comes from patience, not from one clever move.
