Hello Andrew,

I want to express my appreciation for your outstanding website that makes it possible for me to analyze and modify my Sudoku solutions. I attacked (and solved) my first Sudoku puzzle in the Richmond, Virginia, newspaper at Christmas time in 2009; so you see, I am a quite recent entrant into this particular puzzle genre.

Having gotten hooked, I solved the daily Sudokus until around the middle of last year. As a programmer I began to think that creating the puzzles themselves would prove more challenging than simply solving someone elses'.

My computer printed out my first successful 81-digit Sudoku last July. However, creating a 30-or-so digits puzzle by randomly knocking out 50-or-so digits from my Sudokus has turned out to be rather frustrating. It was too easy to generate a redundant (i.e. non-unique) puzzle. But your Sudoku Solver has helped me immeasurably!

Entering my trial puzzles into your solver, I can judge their levels of difficulty by how many of your 35 strategies are needed to solve them. Also, it is relatively easy to see the puzzle combinations that cause trouble (and redundancy) by stepping through your strategies and then tweaking the puzzle distributions slightly to "fix" any difficulties.

Again, thanks so very much for your splendid site!

Best regards,
Bill Harrison
f8bill@gmail.com

Please turn off the auto-tabbing when entering numbers in the small grid. Very confusing and tough to negotiate now.

Key strokes for loading a new Sudoku have changed. The worst is the total loss of entries if the tab key is pressed to leave the last square empty.
Entering a number now also advances the active square making it harder to correct an error using the delete followed by the correct entry.
Please restore the old system.
Thanks,
Bill.

Andrew,

Thanks so much for your sudoku website!

I wrote my own sudoku solving program (in Java) and, to check it out,
used the 50 hardest puzzles from a Will Shortz book.
Since my rules were sufficient to solve them all, I figured I was done.
I also figured that the chaining rules I had read about--and had NOT programmed--just
never really occurred. Wrong!

On vacation (I never do sudoku at home) I ran into an "expert" puzzle
and got as far as follows:
134627985805130060706058010050280030270563840083071520547812090318796452962345178
where I was stuck. When I got home I found that my program was stuck there, too.

So I DO have to look for chaining, which I don't think should be too difficult.
--------

BTW, I like your way of saving the puzzle as a cookie. I hadn't thought of that.

Best,

Marvin Shapiro