31 votes
Accepted

Titanic Tic-Tac-Toe

The first player can always force a win. I wrote this Python script to analyze the tree of possible game states reachable from an empty starting board. No matter what the second player does, the ...
Kevin's user avatar
  • 6,449
19 votes
Accepted

Blindfold Tic-Tac-Toe

You can't do this going second: The strategy going first is: Interestingly,
Deusovi's user avatar
  • 146k
19 votes
Accepted

Noughts and Crosses puzzle

The position is as follows: No two of Eques's counters occupy the same line of 3 (satisfying the never-threatening requirement), and no matter where Knott (O) places their next O, Eques (X) has a ...
Stiv's user avatar
  • 141k
14 votes
Accepted

A Tic-Tac-Toe variant with three marks - winning strategy and chances

Solution Step-by-step deduction If A plays first, then Proof: the crucial realisation is that B can always force A to play in a specific square. WLOG, say A's first move is an $X$. If A's first ...
Rand al'Thor's user avatar
14 votes

Tic-Tac-Toe problem

The answer is no, no one can force a win. Suppose Niels goes first. Henrik can stop Niels from winning as follows: whenever Niels goes in a triangle, Henrik goes in the corresponding coloured triangle:...
Wen1now's user avatar
  • 9,253
13 votes
Accepted

Tic-Tac-Toe Without a Predefined Board

X plays, O plays, X plays as follows: X O X We're now locked on this plane, albeit not uniquely (the O can be in the central or rightmost column). Either way, O ...
BlueHairedMeerkat's user avatar
12 votes
Accepted

What is my favorite brand of pen?

I don't know what it was about the last hint that finally got me to the solution but I have it now. Here's how I moved forward from Stiv's partial solution: finally gives Many thanks to Stiv for ...
xyldke's user avatar
  • 1,773
12 votes

What is my favorite brand of pen?

A partial answer to explain the 'Given...' section. There are several clues in this puzzle to tell us that we should be focussing not on tic-tac-toe, but on the game of... One other important element ...
Stiv's user avatar
  • 141k
11 votes
Accepted

Buzzword Bingo Boss Battle!

So, we are playing misère Tic-tac-toe with the option of taking more than one turn in a row. Seems quite interesting, so let's take a stab at it. The flow of the narrative here is a bit messy, because ...
Bass's user avatar
  • 77.4k
9 votes
Accepted

Pigpen Tic-Tac-Toe

The game: So the winner is... First lets deduce what the words must be: And now we can fill in the grid, turn by turn: And from here, calculating the scores will find that
Beastly Gerbil's user avatar
6 votes
Accepted

Tic Tac Toe Recursive

Alice wins. She starts by playing in the center square of the center board (which we'll call board C). Bob sends Alice over to another board, and she plays in the center of that one. Eventually, Bob ...
Deusovi's user avatar
  • 146k
6 votes
Accepted

Noughts and Crosses and... there's more?

First, as clued in the hint, Looking at the grids in the first row, we note that Interpreting Looking at the bottom row of grids
caPNCApn's user avatar
  • 19.1k
5 votes

Playing tic-tac-toe by submitting your moves in advance

phenomist's user avatar
  • 13.6k
5 votes
Accepted

Tic-Tac-Toe on a Rubik's Cube

They are literally winning words because.. We can see that.. We can list down them as, Now using the same logic for remaning two matches we get.. from where we can identify the other two winning ...
ACB's user avatar
  • 6,731
5 votes

Decision Paralysis

The one with the winning strategy is quite surprisingly First, let us note that First options Case 1 Case 2 Case 2.1
user39583's user avatar
  • 8,968
5 votes

Optimal running-time tic-tac-toe algorithm

"Asymptotic complexity" is a notion that only makes sense when you have some notion of "problem size" that can increase to infinity. The game of tic-tac-toe is always played on a 3x3 board and never ...
Gareth McCaughan's user avatar
4 votes

What is the optimal first move in tic-tac-toe?

There is a nice article analyzing the Tic Tac Toe first move strategy at https://paperandpencilgames.com/2019/02/tic-tac-toe-strategy-tutorial.html To address the reviewers comments, here is the ...
Domosed's user avatar
  • 417
3 votes

What is the ideal strategy in this randomised-goal tic-tac-toe variant?

I spent entirely too much time thinking about this when it was posted, but I still only have a partial answer. Also, this whole answer (and all of its underlying thoughts) were assuming that the game ...
Tim C's user avatar
  • 2,544
3 votes
Accepted

Harary's generalized Tic-Tac-Toe; Winning strategy for Skinny on a 7 x 7 board?

Daniel Mathias has solved this question in a comment on the MSE post, so for completeness I will summarize the entire strategy here. X starts by claiming the center. Up to symmetry, O's response is ...
Mike Earnest's user avatar
  • 32.3k
2 votes

Tic-Tac-Toe Without a Predefined Board

Yes, as long as I didn't interpret you wrong, I believe that player 1 has a forced win: Diagram: Diagram explantion and reasoning: 2. 3. 4.
Jason_'s user avatar
  • 4,093
2 votes

What is the optimal first move in tic-tac-toe?

From experience of playing against kids that don't have the game solved (daughters, ages 5 and 7 at the time of play), starting in the corner gave about 1/3 chance to win and starting in the center ...
Zizy Archer's user avatar
  • 2,150
1 vote

Titanicker Tic-Tac-Toe

There can't be a draw because if the board is full, either you can move the board and get new places to play, or you can't because all positions you can go where already used, and you lose. So the ...
Xoff's user avatar
  • 814
1 vote

What is the optimal first move in tic-tac-toe?

One way to answer this is to consider all 255,168 possible games of tic-tac-toe and record if they result in a win, draw or loss for the starting player and analysing where the first move was for each ...
Ant Kutschera's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible