On Friday I posted this puzzle….

Can you place six X’s on this naughts and crosses board without making three-in-a-row in any direction?


If you have not tried to solve it, have a go now.  For everyone else the answer is after the break.
Here we go…
Did you solve it?
I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.


  1. I got it (and obviously the 90 degree rotation) but it took ages of randomly adding 2 crosses to each row until I occidentally stumbled on the right answer.

    I wonder if there’s any sort of logical way to do it beyond “brute force” ?

    1. With 6 crosses to fit in, clearly there has to be 2 in each row. There are only 3 ways to put two crosses in a row, so that leaves a maximum of 9 options to test, and some of those disappear due to symmetry, etc, so not many options to check.

  2. There was no restriction of “1 cross per cell”, so I just put multiple small crosses inside the same cells. Felt a bit naught-y though.

  3. Given that there were no mentioned restrictions on how you could place the Xs, I just put them all on one place.

    I did also get the official answer.

  4. I wonder if you could extrapolate this to filling (n^2)-n squares in any grid of size n – and if there’d always be just one solution (plus rotations) or if there’d be multiple solutions with larger grid sizes (and if so, if the number of solutions could be determined algebraically)?

  5. I arrived at this answer (mirror image) in less than 10 secs. Then I thought “Where’s the trap”? Obviously 0 can win through the diagonal – so there IS a winner; so there must be a more devious solution, where there is no winner. Next I thought “Hold on. X can never place more than 5 Xs in any game”. So I gave up looking for a smart answer and moved on. Very disappointed.

  6. How could anyone not get this in a nanosecond? I got this right away, but I thought maybe there’s a a better trickier answer. I reckon not.

  7. Richard, Richard, Richard — the rigors imposed by promising a new puzzler every week must be enormous. My sympathies.This week’s challenge took roughly 3 seconds to solve after I finished reading it.

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