About this game
The first game anybody solves
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Nine squares. Three in a row. Tic Tac Toe is the game every child works out on their own, usually in the same order: first they discover the centre, then they discover the corners, then they discover that a competent opponent can no longer be beaten — and they stop playing it forever.
Which is a shame, because the interesting part starts at exactly that point. Once both players are un-loseable, the game stops being about winning and starts being about whether you can make somebody blink. It is also the cleanest possible thing to hand across a table when you have ninety seconds to fill.
Where it comes from
Three-in-a-row games are ancient. Roman children played terni lapilli with three counters each, moving them around a grid once they were placed, and the scratched boards turn up on pavements across the empire. The version with nine fixed marks and a pen took its familiar English name in the nineteenth century.
It also has an odd place in computing history. In 1952 A. S. Douglas built OXO on the EDSAC at Cambridge — a machine occupying a room — so that a person could play tic-tac-toe against it on a cathode-ray display. It is one of the first video games anyone ever made, and the reason it was chosen is the same reason it is a good teaching example today: the entire game tree fits, and a computer can simply check every future.
What this version does with it
The three difficulty levels here are genuinely three different opponents. Easy makes mistakes on purpose, at a rate that gives a child a real chance. Medium plays well and will take a fork if you leave one. Impossible is exactly what it says — it searches the whole game to the end, so the best result available to you is a draw, every time, forever. Beating it is not a matter of skill; there is nothing there to beat.
Neither mark is a letter. Both are drawn as pen strokes, which is why they arrive on the board being written rather than appearing all at once, and why they stay sharp however large the squares get. You can choose your mark, choose who goes first, and keep a running tally against the computer and a separate one for two players sharing a phone.
Thirty seconds to start
- Tap a square to take it. On a keyboard the number keys 1 to 9 read across the board.
- Set your opponent, level, mark and who opens in the settings sheet.
- Pass and play gives two people one device and no computer at all.
The trick that ends most games
The fork: one move that creates two separate threats at once, so blocking either one loses to the other. Almost every genuine Tic Tac Toe defeat is a fork you did not see being set up a move earlier, and almost every genuine win is one you built. Learning to spot the shape — and to answer it by making a threat of your own rather than passively blocking — is the entire remaining depth of the game. The guide lays the common ones out.