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X-treme 23 October - stuck
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sudokuEd
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PostPosted: Mon Oct 23, 2006 12:20 pm    Post subject: X-treme 23 October - stuck Reply with quote

Great puzzles Ruud. Love being able to use lots of cross-over moves - but not enough this time. Any suggestions anyone? Thanks.

Code:
.------------------.------------------.------------------.
| 349   467   3467 | 2     3459  3457 | 3457  1     8    |
| 348   479   2    | 14578 6     1457 | 3459  3457  4579 |
| 348   5     1    | 3478  349   347  | 3479  2     6    |
:------------------+------------------+------------------:
| 145   8     45679| 34567 345   13457| 2     4567  4579 |
| 45    3     4567 | 4567  2     9    | 8     457   1    |
| 12459 12467 45679| 1457  8     457  | 45679 4567  3    |
:------------------+------------------+------------------:
| 12345 124   45   | 9     1345  8    | 34567 34567 457  |
| 7     49    3459 | 345   1345  6    | 1345  8     2    |
| 6     14    8    | 345   7     2    | 1345  9     45   |
'------------------'------------------'------------------'
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Ruud
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PostPosted: Mon Oct 23, 2006 9:13 pm    Post subject: Reply with quote

This X-Treme is much harder than others I've posted.

Here is a hint on how to proceed:

r1c1=3 => r2c2=9 => r8c2=4 => r8c3=9 => r1c3=1 => r1c1<>3

This chain proves that r1c1 cannot be 3.
Something hidden in the down diagonal will help you further.

After a series of steps, you need another tough move.

I'll see you when you get there... Cool

Ruud
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sudokuEd
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PostPosted: Tue Oct 24, 2006 8:47 am    Post subject: Reply with quote

Ruud wrote:
I'll see you when you get there... Cool
So, we meet again! Great hints Ruud. OK - so this is where I'm at this time - another contradiction chain? Have been staring at all the cells with two candidates - but nothing showing. Do I really have to go up to the 3 candidates cells? This is a ripper!

Code:
.------------------.------------------.------------------.
| 49    467   346  | 2     459   3457 | 457   1     8    |
| 348   479   2    | 14578 6     145  | 459   345   459  |
| 348   5     1    | 478   49    347  | 3479  2     6    |
:------------------+------------------+------------------:
| 145   8     45679| 36    345   1457 | 2     4567  4579 |
| 45    3     4567 | 4567  2     9    | 8     457   1    |
| 12459 1246  45679| 1457  8     457  | 4569  4567  3    |
:------------------+------------------+------------------:
| 12345 124   45   | 9     1345  8    | 36    34567 457  |
| 7     49    3459 | 345   1345  6    | 1345  8     2    |
| 6     14    8    | 345   7     2    | 1345  9     45   |
'------------------'------------------'------------------'
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Ruud
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PostPosted: Tue Oct 24, 2006 4:41 pm    Post subject: Reply with quote

The next move is a skewed X-Wing that you will only find in a Sudoku-X

Code:
.------------------.------------------.------------------.
| 49    467   346  | 2     459   3457 | 457   1     8    |
| 348   479   2    | 14578 6     145  | 459   345   459  |
| 348   5     1    | 478   49    347  |-3479  2     6    |
:------------------+------------------+------------------:
| 145   8     45679|*36    345   1457 | 2     4567  4579 |
| 45    3     4567 | 4567  2     9    | 8     457   1    |
| 12459 1246  45679| 1457  8     457  | 4569  4567  3    |
:------------------+------------------+------------------:
| 12345 124   45   | 9     1345  8    |*36    34567 457  |
| 7     49    3459 |-345   1345  6    |-1345  8     2    |
| 6     14    8    |*345   7     2    |*1345  9     45   |
'------------------'------------------'------------------'

Row 9 and the \ diagonal have all candidates confined to 2 columns. Like a straight X-Wing, you can eliminate the remaining candidates from these 2 columns.
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sudokuEd
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PostPosted: Wed Oct 25, 2006 10:52 am    Post subject: Reply with quote

Nice one - love the name too. Is that a positive or negative skewed X-Wing?

Now - next day - next spot. Next hint?
Code:
.------------------.------------------.------------------.
| 49    467   346  | 2     459   3457 | 457   1     8    |
| 48    479   2    | 14578 6     145  | 459   3     459  |
| 348   5     1    | 478   49    347  | 479   2     6    |
:------------------+------------------+------------------:
| 145   8     45679| 36    345   1457 | 2     4567  479  |
| 45    3     4567 | 4567  2     9    | 8     457   1    |
| 12459 1246  45679| 1457  8     457  | 469   4567  3    |
:------------------+------------------+------------------:
| 12345 124   45   | 9     1345  8    | 36    467   47   |
| 7     49    3459 | 45    1345  6    | 145   8     2    |
| 6     14    8    | 345   7     2    | 1345  9     45   |
'------------------'------------------'------------------'
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Ruud
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PostPosted: Wed Oct 25, 2006 2:42 pm    Post subject: Reply with quote

sudokuEd wrote:
Is that a positive or negative skewed X-Wing?

I had a very positive experience when I found it. Very Happy


The next step is X-tremely tough. It is an ALS-xz step.

Column 1 has an Almost Locked Set in cells r123457c1 with digits 1234589. That's 7 digits for 6 cells.
Box 7 has an Almost Locked Set in cells r7c23, r8c2 & r9c2 with digits 12459. That's 5 digits for 4 cells.



Digit 2 can only appear in one of these 2 sets, because it will either be in r7c1 or r7c2. As a result, one of these sets will eventually be locked for the remaining digits.

Scenario 1: r7c1=2 => (Locked Set in box 7) => r8c2=9
Scenario 2: r7c2=2 => (Locked Set in column 1) => r1c1=9

r2c2 can see both these cells and you can eliminate digit 9 from this cell.

There are a few more of these ALS steps ahead. Ready to throw in the towel? Twisted Evil
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sudokuEd
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PostPosted: Thu Oct 26, 2006 12:11 pm    Post subject: Reply with quote

That is a very clever move Ruud. Very worthy of Mr Cool

Now - just have to work out how to find one for myself. No luck so far - but will study up your solving guide on the w-end and try again. So the towel can stay nicely tucked in the corner for a bit longer yet - though it is getting pretty sweaty!

BTW - So good to be able to save a puzzle with SudoCue - and paste in marks. Any chance of making SumoCue be as clever?
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sudokuEd
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PostPosted: Sat Oct 28, 2006 8:49 am    Post subject: Reply with quote

Getting the towel out... Just can't see any more ALS - or anything for that matter Confused
Code:
.------------------.------------------.------------------.
| 9     467   346  | 2     45    3457 | 457   1     8    |
| 48    47    2    | 14578 6     145  | 459   3     459  |
| 348   5     1    | 478   9     347  | 47    2     6    |
:------------------+------------------+------------------:
| 145   8     45679| 36    345   1457 | 2     4567  479  |
| 45    3     4567 | 4567  2     9    | 8     457   1    |
| 1245  1246  45679| 1457  8     457  | 469   4567  3    |
:------------------+------------------+------------------:
| 12345 124   45   | 9     1345  8    | 36    467   47   |
| 7     9     345  | 45    1345  6    | 145   8     2    |
| 6     14    8    | 345   7     2    | 1345  9     45   |
'------------------'------------------'------------------'
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sudokuEd
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PostPosted: Mon Oct 30, 2006 2:38 am    Post subject: Reply with quote

Just threw in the towel and resorted to "hints". Alas - NMH Sad

Does that mean another contradiction chain Ruud? Have looked at all the two candidate cells - but nothing.

Actually, maybe I should download the Beta version - it might do better Rolling Eyes Will edit this if successful.

[edit] Just found this
Quote:
Change and save the Solver Options to enable the new solving techniques.
So beta does find NLS eliminations (maybe the earlier one did too but didn't have enabled).

Gotta go now - but will study later and ask for help if needed.

Thanks for all your help Ruud - so much to learn about this limited variant Smile
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emm
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PostPosted: Mon Oct 30, 2006 4:23 am    Post subject: Reply with quote

I bet this is not the smartest next move, Ed, but it gets you a little way further on.

I really tried to find an ALS - I'm hoping this is a valid contradiction chain.

r9c2=4 => r9c9=5

r9c2=4 => r2c2=7 => r1c2=6 => r1c3=4 => r1c5=5 => r1c7=7 => r3c7=4 => r8c7=5

=> r9c2<>4 which gets you to here

Code:

.------------------.------------------.------------------.
| 9     467   346  | 2     45    3457 | 457   1     8    |
| 48    47    2    | 14578 6     145  | 459   3     459  |
| 348   5     1    | 478   9     347  | 47    2     6    |
:------------------+------------------+------------------:
| 145   8     45679| 36    345   1457 | 2     4567  479  |
| 45    3     4567 | 4567  2     9    | 8     457   1    |
| 1245  246   45679| 1457  8     457  | 469   4567  3    |
:------------------+------------------+------------------:
| 2345  24    45   | 9     1     8    | 36    467   47   |
| 7     9     34   | 45    345   6    | 1     8     2    |
| 6     1     8    | 34    7     2    | 345   9     45   |
'------------------'------------------'------------------'
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sudokuEd
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PostPosted: Mon Oct 30, 2006 11:33 am    Post subject: Reply with quote

Aarggh - Ruud and emm - you're messing with my head.

emm doing it I can understand and forgive since we beat you in netball (if you are the emm with the nice round vowels Wink ).

Ruud doing it I can understand - because that's what coaches do.

But why are you both doing it at the same time Question Must be some sort of complex, sinister plot - perhaps
sinister riddler wrote:
NLS . Question Exclamation . Arrow ALS


OK. Now getting serious.

emm wrote:
I'm hoping this is a valid contradiction chain.

Don't think so unfortunately. I think the second chain still has r89c7 with {135} available. So, not sure how you can lock in the 5 there. But I could be wrong 'cause I find it very tough to 'see' that many steps ahead. BTW - I think you missed a step also to be able to show that r1c3=4 ( r78c3 = [53])

SudoCue wrote:
Two Almost Locked Sets sharing digit 7 eliminate candidate(s) for digit 5
I can't understand how the two ALS's share digit 7. This is the way it looks to me

1. One ALS in r45689c4 with digits 134567. 6 digits, 5 cells.
2. One ALS in r23c7 + r2c9 with digits 4579. 4 digits, 3 cells.
The only way those two ALS see each other is through D/.

But how they "share digit 7". Why can't 7 be in r5c4 when 7 is in r3c7? If 7 can be in both spots, then 7 is not "restricted common".

There must be another way of interpreting SudoCue I can't see yet. Can anyone clarify? Thanks.
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PostPosted: Mon Oct 30, 2006 6:16 pm    Post subject: Reply with quote

Actually, I found a more appropriate ALS-xz pattern in your grid, which can only be found in a Sudoku-X.

Here it is:



Isn't it a beauty? Digit 3 is shared on a diagonal...
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sudokuEd
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PostPosted: Tue Oct 31, 2006 7:10 am    Post subject: Reply with quote

Now that I can understand - it is a beauty. It made perfect sense as soon as you pointed it out .

I really like this ALS technique - just can't find them for myself yet.

Mind you, eliminating that 5 doesn't seem to get us any further - just also lose a 5 from r8c7. Can't see anything from there - unless I'm missing something. emm's contradiction idea still doesn't seem to help Sad

The "hints" again points out the ALS move which I can't understand. When all the solver options are enabled it gets really scary with "Medusa" something. So....totally out of my depth there.

But have something to improve in that looks really promising. Time to practice on some friendlier X-tremes - perhaps the ones that don't say "unfair"! Thanks coach Smile
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emm
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PostPosted: Wed Nov 01, 2006 2:37 am    Post subject: Reply with quote

Ruud, you're a wizard at making things clear. Your coloured dots light the ALS up like a runway strip! Very Happy

Ed, my moves weren’t so much missing as implied !

r9c2 = 4 -> r9c7 = 1 -> r8c7 <> 1
r9c2 = 4 -> r1c3 = 3 -> r8c3 = 5 -> r8c7 <> 5
If I’d been able, I’d have done a nice loop but it was too complicated.

Thanks for the hint about the other ALS - I see what you’re saying about the 7s.
If 7 is restricted common because of the diagonal, then is this also true?

Code:

.------------------.------------------.------------------.
| 9     467   346  | 2     45    3457 | 457   1     8    |
| 48    47    2    | 14578 6     145  | 459   3     459  |
| 348   5     1    | 478   9     347  | 47    2     6    |
:------------------+------------------+------------------:
| 145   8     45679| 36    345   1457 | 2     4567  479  |
| 45    3     4567 | 4567  2     9    | 8     457   1    |
| 1245  246   45679| 1457  8     457  | 469   4567  3    |
:------------------+------------------+------------------:
| 2345  24    45   | 9     1     8    | 36    467   47   |
| 7     9     34   | 45    345   6    | 1     8     2    |
| 6     1     8    | 34    7     2    | 345   9     45   |
'------------------'------------------'------------------'


A = r1c2 r2c12
B = r6c3678
X = 7 ( D\ r2c2 and r6c6)
Y = 6
=> r6c2 <> 6

So now we have


Code:

.------------------.------------------.------------------.
| 9     6     34   | 2     45    3457 | 457   1     8    |
| 48    7     2    | 1458  6     145  | 459   3     459  |
| 348   5     1    | 478   9     347  | 47    2     6    |
:------------------+------------------+------------------:
| 145   8     45679| 36    345   1457 | 2     4567  479  |
| 45    3     4567 | 4567  2     9    | 8     457   1    |
| 1245  24    45679| 1457  8     457  | 469   4567  3    |
:------------------+------------------+------------------:
| 2345  24    45   | 9     1     8    | 36    467   47   |
| 7     9     34   | 45    345   6    | 1     8     2    |
| 6     1     8    | 34    7     2    | 345   9     45   |
'------------------'------------------'------------------'


PS : Your turn! Very Happy

PPS : Do I know you from another persona or are you a lurker in the other forum?
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sudokuEd
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PostPosted: Wed Nov 01, 2006 5:52 am    Post subject: Reply with quote

emm wrote:
Ed, my moves weren’t so much missing as implied !

Thanks for pointing that out. I've only ever been a Killerholic - this is my first foray into any Killer variants - so not familiar with the syntax etc.

I've finally been able to convince myself that r9c2<>4 (using SudoCue rather than my head).
r9c2=4 => r9c9=5 => r9c7=1 =>r8c7=4

r9c2=4 => r2c2=7 => r1c2=6 => r1c3=4 => r1c5=5 => r1c7=7 => r3c7=4

= two 4's in c7=> r9c2<>4.

I'm still not sure of the way you did it - but at least we agree on the result now - and with your marks pic. So - at least we're making some progress.

emm wrote:
Thanks for the hint about the other ALS - I see what you’re saying about the 7s.
If 7 is restricted common because of the diagonal, then is this also true?
I don't understand the other hint about the 7's. It may be true - but it seems to be a different pattern than Ruud's ALSxz and I can't understand how it works.

I have the same problem with your suggestion of the 7's on D\ . To me the 7 is not "restricted common" because 7 could be in both ALS at the same time eg. if r6c6 was 7, could have 7 in r1c2. So the 6 is not forced to be in r1c2. Similarly, when r6c6 = 7, the other 3 cells in ALS B have {4569} available - so 6 is not forced to be there either.

Please try again if I havn't got this right.

PS. lurker
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