Non-Unique Solutions in Publications...

Chigger

Greetings, all...

Like many of y'all, if I'm not creating my own sudoku, I'm snaggin' cheap books of sudoku just for practice... Hey, several hundred for a few bucks, and it's something I can always lug with me... Smile

Well, I picked up at Wal-Mart volume 3 of "Sudoku", as referenced on this page:

http://www.sudokurewards.com/

It looks like it was published in New York, but was originally printed in the UK...

Alright, enough of that... Here's the qualm. Was smoking along on the "easy" puzzles (it has some of varying levels of difficulty), usually hitting 5-7 minutes (if uninterrupted) on each one, if uninterrupted, when I ran across the following puzzle:

.9. ..3 26.
... ... .3.
3.2 .5. ..4

21. 6.. 4..
.8. 3.5 .9.
..3 ..4 .81

4.. .3. 8..
.2. ... ...
.39 2.. .7.

I moved right along, filling in the blanks until I ended up with:

195 473 268
846 192 537
372 856 914

217 689 453
684 315 792
953 724 681

461 .37 82.
728 .61 34.
539 248 176

What the......? Sure looks like there are 2 different solutions to this one... Ran it through SadMan Sudoku (kudos!!) and it identified 2 different solutions too.. And when asking it to solve it, it filled in r7c4 with a 5 as "a guess!" (presumably, it picked 5 only because it was working through the numbers in ascending order)... Lovely...

This is the kind of thing that frustrates me... A novice Sudoku solver could get there and think they messed up, only to start over... And keep getting stuck over and over... Or guess a 5 or 9, fill in the remainder, then wonder why their solution doesn't match what's in the solution section...

Have y'all seen this in publications before? I've done a ton of 'em, and this is the first one I've found.

Finally, is there a way to make this a unique solution besides providing 1 of the remaining 5s or 9s or completely changing the clues?

- Bert

Ruud · Site Admin

Hi Bert,

about your first question: Has this happened before?

Yes. Many times. It is not always noticed, because many people solve these puzzles by guessing, once they're stuck, so when they find a solution, that must be it. My local newspaper has been publishing invalid sudokus with upto 46 solutions, with only a few people noticing. Most other readers just loooved these new puzzles.

Your second question:

The only way to make this puzzle a unique one is providing a clue in 1 of the 4 remaining cells. They form a "deadly" pattern, i.e. a rectangle in 2 rows, 2 columns and 2 boxes with 2 digits in the corners.

Ruud.
_________________
Meet me at sudocue.net

Chigger · Posted: Mon Dec 19, 2005 7:19 pm Post subject: