ST Sudoku Very Hard 315

[Misstoddler]

Hope it's ok to post a non-crossword query on here...

I was very pleased with myself for completing today's Very Hard sudoku as it's rare I complete it.

To celebrate, I thought I would sms the three correct numbers but the reply text said I was incorrect.

I very carefully double-checked every horizontal and vertical line and every cube to ensure no numbers were duplicated. All seemed perfect.

So two queries:

1. Is it possible to have more than one correct solution for a Sudoku?

2. My three shaded numbers were 333. If someone has completed it, could they pls tell me whether they have the same? Maybe there is a technical problem at ST and the wrong message is being sent out. This would be annoying as I would then have wasted �1 with zero chance of winning!!

[SpodoCommodo]

I get the same answer 333, and if you feel like cheating then this sudoku solver

http://www.strictlysudoku.com/sudoku-solver.ph p

says that there is only one solution (giving 333 for the shaded numbers) and rates it as fiendish.

[Misstoddler]

Hi SpodoC,

After posting the above, I searched the Net for help on Sudoku and came across that link and agree it comes up with the same answer.

I'm really cross with the ST as, again rarely, I completed the Very Hard two weeks ago, texted my answer at 10 am only to get a reply indicating my anwer had been submitted outside of opening hours (which wasn't true).

Out of curiousity, I texted it again in the afternoon and got the same reply.

So I assume that was another �2 wasted!!! Quite a good scam!!!

[SpodoCommodo]

I can't help you with the ST as regards its propriety because I never phone or send in puzzles for prizes, I just do them for the brain exercise.

[etwills]

> 1. Is it possible to have more than one correct solution for a Sudoku?

No, there must -by definition- be one solution.

In the harder puzzles, a case exists where you have to go looking to rule out candidate digits for the cells, rather than seeking cells with a clear right answer. The "only one solution" rule can be used to rule (some) digits out when multiple solutions to the puzzle would result if that digit was assumed to be part of the answer.

Hope this helps!
W.

[Misstoddler]

Thank you W. That is helpful, yes.

[etwills]

I'm glad. There are surprisingly many other rules for cutting down the lists of candidate digits for each cell, so I don't think I've spoilt anything letting you know this is one of them.

Good luck finding them all out. The satisfaction is *well* worth the effort!

*SPOILER ALERT* ...if you still have time to (or already have), grab a copy of the Metro. The "Challenging" puzzle in today's has three solutions if you attempt it by brute force but you can rule two of them out in this way, leaving just one answer which is valid.