Cognitive Daily

Here in Tuscany, the Munger family has rented a vacation house for a couple of weeks. Typically the day’s biggest event is preparing dinner. Otherwise we generally just lounge around the house, admire the view, read, or converse over a glass of wine.

Today we thought we needed a project, so Nora and I decided to try and make our own Sudoku puzzle. It’s actually more difficult than you might think. You can’t just randomly fill in squares in a grid to make a Sudoku puzzle that works. Then it’s another challenge to create a set of clues that will result in one unique solution.

After several hours’ work and several sheets of scratch paper, we think we’ve come up with a puzzle that isn’t trivially easy.

But we’re rather close to the project, so perhaps the puzzle we made isn’t challenging enough. Or maybe we made a mistake and our puzzle doesn’t have a single solution. So we decided to put our puzzle to the readers of CogDaily. Here’s what we came up with:


Unfortunately we’re not smart enough to create an interactive online puzzle, so if you’d like to try it you’ll have to print the puzzle out and fill it in by hand (click to open in its own window for easy printing!). Once you’re done, let us know how we’ve done in the poll below.

If you’re a Sudoku novice, the instructions are simple. Just fill in the remainder of the grid so that every row and every column has every digit from 1 to 9 with no repeats. In addition, every bold-outlined 3 X 3 square must also contain each digit from 1 to 9 with no repeats.

Do you have any suggestions for how to improve our puzzle? Have you ever tried to make your own Sudoku? Let us know in the comments.


  1. #1 Flaky
    June 28, 2007

    The puzzle is solvable using only scanning, i.e. locating squares that can admit only one number as other numbers are ruled out by numbers in other squares on the same row or box. A more difficult puzzle would require other techniques as well.

    I did write a sudoku generator once. It’s actually quite an interesting problem. Generating full sudoku grids is pretty easy by picking random numbers and essentially using trial and error to eliminate illegal grids (and speeding up the algorithm by cleverly exploiting the constraints of the game). But removing numbers to create the puzzle is a bit trickier. What I tried was to remove numbers randomly, until not a single number could be removed without increasing the number of solutions. The results were ok, but mostly not among the hardest possible.

  2. #2 dermot
    June 28, 2007

    Yes, it isn’t very difficult, but at least it has a unique solution. I have a Sudoku solver and generator written in Excel (VBA), if you are interested.

  3. #3 Michelle
    June 28, 2007

    The puzzle wasn’t very hard, as stated before it didn’t need advanced techniques to solve. But, considering it wasn’t generated by a computer, it was pretty good :)

  4. #4 Aaron Couch
    June 28, 2007

    This was a great little diversion from work this morning. I found it to be average, but like Michelle said above, it is impressive that it was generated without a computer, especially considering that it has one unique solution. Now what I’d really like to see you and Nora do is make one of the 16×16 Sudoku puzzles; I’m sure that would keep you busy for a while.

  5. #5 Scott Spiegelberg
    June 30, 2007

    Or make a sidoku. I’d go with the chromatic run, though I imagine there is some challenge in creating the Congressional District-like boxes of the 7-note sidokus.

  6. #6 JF
    July 1, 2007

    hey dermot,

    you said you have a sudoku generator/solver written in VBA code? do you mind i take a look at it? it sounds pretty interesting. thanks!

  7. #7 Nachiket Vartak
    July 2, 2007

    One way to evaluate a Sudoku puzzle’s diffulty that I use it to see how fast a given algorithm solves it.

    Even a simple Javascript based solver could get through this one instantaneously.

    For people who are looking for Sudoku solver code…take a look here

  8. #8 Norman Costa
    July 4, 2007


    It was not trivially easy, but not too hard either. A nice diversion. Creating it by hand wins my admiration.

    Norman Costa

  9. #9 Svaj Malizo
    July 27, 2007

    I add to what others have already said. Average difficulty, admirable task.

    The only problem I had with this is thinking you were in Tuscany and you were doing this! You could have done this on the plane, or back home, or anywhere else! Were you really there so long as to get bored?

    For me, it’s one of those places where I could get Stendhal syndrome from food, art, music, architecture, poetry or natural landscapes.

    I’d have so many seizures I couldn’t possibly think about doing a sudoku puzzle, let alone MAKE one.

    But well, I guess there’s people for everything.

    Be happy and enjoy the weather (wherever you are),

    The Svaj

  10. #10 Sudoku Maniac
    March 19, 2008

    same here, even I solve sudoku puzzles when I got nothing to do.. well solving Sudoku becomes more easier if you have color coding, count of numbers etc.. try