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Ultimate Tic Tac Toe is played on 3x3 setup of regular Tic Tac Toe boards.

You can try it at https://ultimate-t3.herokuapp.com/

Rules:

Playing on a spot inside a board, determines the next board in which the opponent must play their next move. The goal is to win a three in a row boards. You can play your next move at any board if you are directed to play in a full board or a board that has been won.

example:                                  

the game has been solved and has a winning strategy for the first player (paper, implementation) If the last rule is excluded. That is, if a player that is directed to play at a board that has been won but is not full yet, must play at that board.

With the rule that directing to a won board allows the opponent to play at any board, the game is apparently unsolved. This was mentioned on the site some years ago.

I known of computer implementations of the game that use Monte Carlo or similar methods. Are there known strategies that a human can apply and use? Something like favorable or recommended openings for 1st player, and responses for 2nd player?

0

One way to find strategies is to look at papers that researched the game. For example, AI Approaches to Ultimate Tic-Tac-Toe [paper] consider the following situations:

heuristic#2 takes into consideration many more features of the given board: small board wins add 5 points, winning the center board adds 10, winning a corner board adds 3, getting a center square in any small board is worth 3, and getting a square in the center board is worth 3. Two board wins which can be continued for a winning sequence (i.e. they are in a row, column or diagonal without an interfering win for the other player in the third board of the sequence) are worth 4 points, and a similar sequence inside a small board is worth 2 points. A symmetric negative score is given if the other player has these features

(heuristic#4) builds upon the previous heuristic, but adds:

if you are sent to a small board that is full or won you can play anywhere, so that add 2 points to the heuristic (and -2 for the other player)

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  • Why would you care about winning the center board when it isn't that critical of a square in normal tick tack toe?
    – Joe W
    Jul 4 at 15:50
  • 1
    The middle board is the strongest since it involves in the most "winning lines". The middle square is part of 4 winning possibilities, Corners are part of 3, and edges are only part of 2.
    – Cohensius
    Jul 4 at 15:59
  • But it is also one of the easiest to block a corner spot gives your opponent more opportunity to make a mistake.
    – Joe W
    Jul 4 at 16:13
  • Honestly when you play in a corner there is only 1 out of the 8 possible moves that will prevent you from controlling the board and winning. This also applies to a game of ultimate tick tack toe as well.
    – Joe W
    Jul 4 at 17:34
-1

I am not an expert but here is my 2 cents:

  • Recommended opening for 1st player: the middle of the the middle board.

  • Try not to let your opponent play in the middle board. Do it by completing 3-in-a-row without the middle in the non-middle boards.

  • focus on the boards that matter: I have seen games where one player had won 5 boards but lost.

-1

I would treat the larger board like a single game of tic-tac-toe and play like you are trying to win a single game.

https://www.wikihow.com/Win-at-Tic-Tac-Toe

Most experienced tic tac toe players put the first "X" in a corner when they get to play first. This gives the opponent the most opportunities to make a mistake. If your opponent responds by putting an O anywhere besides the center, you can guarantee a win.[1]

For me I would start by trying to win one of the corners and after that react based on what my opponent does as if you win a corner you should at worst be able to force a draw.

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  • Doesn't that ignore the rule that the position your opponent played in the smaller board determines which of the smaller boards you have to play with your next move? So if you play in the top right corner of the top right board as X, your opponent plays in the centre of that board (since you just forced them to play top right board), forcing you to play your next move on the centre board. Your opponent needs to let you move back to the top right board by playing top right on a sub-board.
    – Andrew
    Oct 6 '20 at 18:57
  • @Andrew I am not saying to completely ignore the smaller boards but you if you get a corner and your opponent gets the center you are still better off as you will have more options at getting a win overall if you have a corner than if you have the center. In truth if that situation happens the game should end in a draw.
    – Joe W
    Oct 6 '20 at 18:59
  • This is very weak strategy. Have you got much experience in this game?
    – Cohensius
    Jul 4 at 11:05
  • @Cohensius Please explain why you think this is a weak strategy, I have not had any bad experience with this as that.
    – Joe W
    Jul 4 at 15:49
  • @JoeW, please try to play few games using your advice, you will see it is a losing strategy. Can try it here: ultimate-t3.herokuapp.com
    – Cohensius
    Jul 5 at 5:56

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