Most of us learn tic tac toe early in our life. Also, it is easy to find an optimal strategy for playing.

How about Quantum tic tac toe? What is the optimal strategy for playing it?


On a player's turn, instead of placing one large mark in one square, they place two smaller 'quantum' marks in two different squares. Moves are also marked with the number of the turn they occured, so the first player would write X1 in two different places on the board. The two squares that have any particular move are called 'entangled'. Multiple small marks can be placed in one of the larger squares.

Suppose that the top-left square holds X1/X5, the center square contains X5/O4, and the right-hand square contains O4/X1. This forms a cycle of entangled squares. These cycles can be any length above two.

When there exists a full cycle of entangled pieces, the player who did not complete the cycle (in this case X5 formed the cycle, so the O player) chooses how to resolve this cycle. Suppose he elects for the top-left square to hold X5. Then there is only one possibility for the square for X1, and thus only one for O4. When a cycle is resolved, write the resolved 'classical' characters in the normal size.

Also, when a cycle is resolved, it may result in hanging chains. Suppose that the centre square from the previous example was actually X5/O4/O2. When the cycle is resolved, there is now only one possibility for the O2, so that move can also be resolved.

To win, a player must, just like standard Tic Tac Toe, create a three-in-a-row of classical (not entangled) moves.

  • 3
    $\begingroup$ Hi, @georgemenoutis! Puzzles posted here shouldn't rely on external resources that can change or disappear without notice, so please include the rules in the question (with proper attribution) instead of just posting a link. Thanks, and happy puzzling! $\endgroup$
    – Bass
    Commented Jan 14, 2020 at 10:48
  • $\begingroup$ @GeorgeMenoutis I've added in some rules to the question based on the Wikipedia link. If I haven't understood the game correctly, please feel free to edit them. $\endgroup$
    – ZanyG
    Commented Jan 14, 2020 at 12:49
  • $\begingroup$ (At) Bass Thank you for the clarification. @ZanyG Thank you for the effort of writing the rules down. I have actually played this game a few times and I confirm your description is accurate. $\endgroup$ Commented Jan 14, 2020 at 13:33
  • $\begingroup$ @GeorgeMenoutis Coolio. $\endgroup$
    – ZanyG
    Commented Jan 14, 2020 at 13:53
  • 3
    $\begingroup$ A quick google search results in this answer: boardgames.stackexchange.com/questions/7085/… $\endgroup$
    – hdsdv
    Commented Jan 15, 2020 at 2:15


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