Tic Tac Toe

How to never lose at Tic Tac Toe

Tic Tac Toe is a solved game, which means perfect play by both sides always ends in a draw. Since you are X and move first on Inkplay, you hold the advantage: you can never lose if you follow a simple rule set, and you can beat the weaker difficulties outright. The single most important decision is your first move: take a corner, not an edge. A corner opening gives you the most ways to build a line and quietly sets traps that a careless opponent walks straight into on the following turn. The game is also tiny in a way that is fun to know: counting move orders, there are exactly 255,168 possible games, collapsing to 26,830 once rotations and reflections merge. Small enough for a machine, or a motivated human, to know all of it.

How to beat Easy and Medium

The Easy computer moves at random and Medium only blocks your immediate wins, so both can be beaten by creating a fork, a position where you threaten two separate lines at once and your opponent can only block one of them:

• Open in a corner; if the computer replies anywhere but the center, you can usually force a fork.
• Always take a winning move when you have one, and always block the computer's three-in-a-row threat.
• Set up two intersecting threats that share one empty square. That shared square is your fork.
• Against Medium, prefer moves that block its plan and build toward your own line at the same time.
• When you play second, grab the center: it sits in four of the eight possible winning lines.

Here is the classic trap played out. Open in the top-left corner. Suppose the computer takes the center, the strongest reply. Answer in the bottom-right corner, so your two marks bracket the long diagonal. If the computer now grabs the remaining corner, it has already lost: you take the bottom-left, and suddenly the bottom row and the left column both threaten to complete. One block cannot cover two lines. The only saving reply to your opposite-corner setup was a quiet edge square, and quiet edge moves are precisely what the weaker difficulties never find. Run this sequence a few times and watch how often the corner grab appears; the fork practically plays itself. And if the computer skips the center entirely on its first reply, your job gets easier still: take the center yourself, and with the middle plus two corners in hand you can normally manufacture two threats inside the next two moves.

Why Hard can never be beaten

The Hard computer plays perfectly, evaluating every possible continuation all the way to the end of the game, a tree small enough to search completely. Because Tic Tac Toe is a guaranteed draw under perfect play, the best result you can force against Hard is a tie. If you make even one inaccurate move it will punish you at once, so treat every game against Hard as a puzzle in not losing rather than in winning. It is genuinely useful practice: the habits that draw against Hard, blocking early, refusing bad edges, seeing forks a move ahead, are exactly the ones that win instantly on Medium.

Origins, Romans, and Tinkertoys

Games of three-in-a-row date back to ancient Rome, where grids for a game called terni lapilli were scratched into paving stones across the empire, though scholars suspect many of those boards belonged to its cousin three men's morris, in which the pieces move around after being placed. The name noughts and crosses is the traditional British term, a nought being the zero-shaped O. The game's small size made it a landmark in computing history: in 1952 A.S. Douglas at Cambridge wrote OXO, a perfect noughts-and-crosses player for the EDSAC computer and one of the earliest video games ever made. In the 1970s, MIT students led by Danny Hillis went the other way and built a computer out of Tinkertoy parts that plays the game flawlessly, a wooden contraption that ended up in a museum. And the 1983 film WarGames closes on a military computer learning from tic-tac-toe that some games cannot be won. Bigger cousins like Connect Four, Gomoku, and Ultimate Tic-Tac-Toe extend the same line-making idea onto larger boards, where the guaranteed draws finally stop.