Ultra hard Sudoku

Oulu · **Posted:** Tue Feb 22, 2011 00:54:01 am

It is claimed this Sudoku is the most difficult one if special Sudokus are not considered. Would you like to take up a challenge and (try to) solve this one?

It's not so difficult. Even I could solve it. :wink:

admin · **Posted:** Tue Feb 22, 2011 01:03:16 am

I simply do not understand these things, but know many do.

I seems to me that many members have Windows 7 which comes with "Snipping Tool" build in, and a little pen icon along with it, so adding a simple hand drawn number is a cinch.

I have just taken a wild guess below .. almost certainly WRONG, but other members can do this if they wish!

Oulu · **Posted:** Tue Feb 22, 2011 01:11:32 am

That's correct. I have got the solution showing the right order to fill in the numbers.

First nine numbers are pretty simple, but the 10th is far more difficult.

Alastair · **Posted:** Tue Feb 22, 2011 03:26:02 am

It can be solved just using the basic principles of completion so it is not the most difficult sudoku.

Oulu · **Posted:** Tue Feb 22, 2011 04:09:56 am

The page where I found it claimed so, but it wasn't "ultra hard". It is anyway worth trying. But not for beginners!

I can give the link to the solution if someone needs it.

GlenStephens · **Posted:** Wed Feb 23, 2011 02:01:15 am

We need to work out a way to do these in a thread.

figmente · **Posted:** Wed Feb 23, 2011 07:28:00 am

It is not a valid Sudoku puzzle, it has multiple answers.

Oulu · **Posted:** Thu Feb 24, 2011 00:40:53 am

Could you give one (answer) I can compare to the one I have?

figmente · **Posted:** Thu Feb 24, 2011 08:13:00 am

285469173
417325869
369187254
198536427
674298315
532714986
751843692
923651748
846972531

285469731
417325869
369187254
198536427
674298315
532714986
741853692
953672148
826941573

285469731
471325869
369187254
198536427
647298315
532714986
714853692
953672148
826941573

clay11 · **Posted:** Thu Feb 24, 2011 15:45:55 pm

Wow! I was happy to get one of the answers, I don't know how you managed to find three. Nicely done!

Oulu · **Posted:** Thu Feb 24, 2011 18:37:20 pm

Figmente, it would have been useful, if you had used different colours to mark those numbers which differ.

Clay11, which one you came up with? I have got the third one.

Now there are four members who have solved this "ultra hard sudoku".

clay11 · **Posted:** Fri Feb 25, 2011 02:00:11 am

Also the third one.

Clay

figmente · **Posted:** Fri Feb 25, 2011 07:26:56 am

This much is clear:

285 469 XXX
XXX 325 869
369 187 254

198 X36 4XX
6XX X98 31X
532 714 986

XXX 8X3 69X
9X3 6XX X48
8X6 9XX 5XX

I suspect that there exist multiple choices for all the Xs.

hatter · **Posted:** Fri Feb 25, 2011 08:44:00 am

no wonder I got stuck

:mrgreen:

will stay with the Evening Standard Su-doku from here on !

clay11 · **Posted:** Fri Feb 25, 2011 09:34:10 am

I am thinking there is a forced next step, but I have to find it.

Clay

clay11 · **Posted:** Fri Feb 25, 2011 10:00:54 am

I now have looked, and have to agree that is an invalid puzzle with multiple solutions. Somewhere along the way, I made an invalid conclusion and this led to one of the possible correct solutions that I came up with. There is no forced next step from this point.

Clay

Oulu · **Posted:** Fri Feb 25, 2011 18:21:40 pm

Don't blame me. I found it on Bulls Press' website - in fact on its Finnish subsidiary's website, but the same "ultra hard sudoku" can also be found on the UK website.

http://www.bullspress.co.uk/united-king ... rd-Sudoku/

It clearly states: "This is by far the most difficult version of your regular Sudoku, without comparison. Only recommended for the very sharpest of brains!"

I disagree with that.

Oulu · **Posted:** Fri Feb 25, 2011 23:25:14 pm

This one was quite tough

clay11 · **Posted:** Sat Feb 26, 2011 10:47:50 am

4X5 XX7 81X
X8X X5X XXX
1X9 X8X X75

XX3 816 5XX
946 235 781
518 974 2XX

XXX 5X8 1XX
X51 XXX 6X8
8X4 X2X X5X

This much wasn't easy, but now I'm stuck. I don't see the next logical step. If someone can explain what I should do from here, that doesn't involve guessing, I'd really appreciate it.

Thanks,

Clay

Oulu · **Posted:** Sat Feb 26, 2011 18:56:02 pm

These two X cannot be either 1 or 2, so they go there X,

4X5 XX7 81X
X8X X5X XXX
1X9 X8X X75

XX3 816 5XX
946 235 781
518 974 2XX

XXX 5X8 1XX
X51 XXX 6X8
8X4 X2X X5X

which gives:

4X5 XX7 81X
X8X X51 XXX
1X9 X82 X75

XX3 816 5XX
946 235 781
518 974 2XX

XXX 5X8 1XX
X51 XXX 6X8
8X4 X2X X5X

It was very difficult to find this out.

pandadog28 · **Posted:** Sat Feb 26, 2011 20:26:45 pm

You do have to guess im afraid and be prepared to start again like a good Suduko wants you too.

It took me 11 tries.

Oulu · **Posted:** Sun Feb 27, 2011 01:01:12 am

A long thinking chain resulted to a conlusion that green Xs must be 3 an 9, so 1 and 2 went up.

Of course if the thinking chain is long, it is possible to make an error and with luck get the correct answer, but probability to this is usually quite low.

Oulu · **Posted:** Sun Feb 27, 2011 01:21:45 am

This one was quite nice. It wasn't too hard ("vaikea").

selvedge · **Posted:** Sun Feb 27, 2011 02:27:40 am

There should never be a time to guess a number. Every number is available through comparison, evaluation logic.

clay11 · **Posted:** Sun Feb 27, 2011 15:58:45 pm

Oulu wrote:

This one was quite nice. It wasn't too hard ("vaikea").

Yes, a nice puzzle. Here is the answer...

284 673 519
931 258 674
756 914 832

345 187 296
679 532 481
812 469 357

163 745 928
527 896 143
498 321 765

Oulu · **Posted:** Sun Feb 27, 2011 18:56:35 pm

clay11 wrote:

Yes, a nice puzzle. Here is the answer...

That's correct.

Oulu · **Posted:** Sun Feb 27, 2011 19:00:16 pm

This is a nasty one (as symmetric sudokus usually are). The two first numbers were simple, and the numbers indexed 1-7 more or less hard.

I got this far only. I have to try it again later.

Oulu · **Posted:** Sun Feb 27, 2011 23:33:06 pm

I have to take my words back in saying this sudoku is hard from this point on. I was not at my best last night, I guess.

From here on it is quite simple. But to get at this point it may be difficult. So I would like to explain how I got to it, and I think it will also explain how I solved the difficult point of *****-sudoku.

You just have to find out the circled numbers can only be 4 and 9. On right the correct numbers are 1 and 3. Now I don't understand why the 3 has the index 10, since it could be #3.

So the fifth row from top is: 183 652 947

Alastair · **Posted:** Mon Feb 28, 2011 01:12:06 am

Oulu,

I found another solution to your last sudoku.

Also, the 4s and 5s in the left three columns can be interchanged.

Alastair

Oulu · **Posted:** Mon Feb 28, 2011 04:51:54 am

Alastair, fine! The solution is different.

This is the solution for the ***** one.

Oulu · **Posted:** Mon Feb 28, 2011 19:25:09 pm

If I can remember correctly, this one is quite tough. I can't see any other reason for I have saved it.

MrSamoa · **Posted:** Thu Mar 03, 2011 05:54:07 am

It was challenging!

Oulu · **Posted:** Thu Mar 03, 2011 18:21:15 pm

That's correct, MrSamoa.

Oulu · **Posted:** Thu Mar 03, 2011 19:16:07 pm

What about this one? Is it tough? I can't remember.

MrSamoa · **Posted:** Fri Mar 04, 2011 00:48:21 am

Not too bad

clay11 · **Posted:** Sat Mar 05, 2011 17:36:02 pm

Oulu wrote:

What about this one? Is it tough? I can't remember.

Not too hard...

826 341 975
793 586 124
145 927 836

487 615 293
259 834 617
361 279 458

972 458 361
538 162 749
614 793 582

Oulu · **Posted:** Sat Mar 05, 2011 19:02:45 pm

If you get a solution which meets the rules, then it must be correct as you have, though there can be multiple solutions as seen.

Here's a new one from today's newspaper. I haven't solved it yet.

Oulu · **Posted:** Sun Mar 06, 2011 01:27:34 am

Oulu wrote:

Here's a new one from today's newspaper. I haven't solved it yet.

That was easy!


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Ultra hard Sudoku

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