The New Sudoku Players' Forum

[georgers]

It's been 5 days.... I've sold other very hards but this one.... *!$**!£$

Anyone prepared to waste their time and save me from concussion?

6*7 2** 3**
4** 8** **6
59* 76* ***

9** 6** 8**
17* *** 642
**6 1** **9

*** *81 *63
861 **2 **5
**9 **6 1**

Any hint gratefully accepted: the x-wings I've found didn't seem to help -- perhaps I still haven't grasped quite how they work.

Thanks in advance...

[Animator]

There are two intresting groups of numbers in box 3 (one of 3 numbers (5, 7, 9) and one of 4 numbers (1, 2, 4, 8)).

I suggest you take a really good look at box 3. (I'm not sure if you are familiar with the technique that is required or not... if you are not then I (or someone else) will explain it a bit more)


When you are done with that you need to look at column 8. You will find a similar thing in it (same technique, different numbers).

When you found it then you can fill in two cells in column 8

[georgers]

I am amazed that what was so opaque for so long for me (at least it felt like forever) was clearly so easily apparent to you. Thank you -- your hint resolved matters speedily.

Makes me want to ask whether YOU ever get stuck, and whether there are any techniques you use for spotting X-wings, multiple possibles etc.

Or is it just practice and confidence?

Anyway, many thanks again: the ringing in my ears is already lessening!

George
(georgers1@gmail.com)

[joolslee]

Makes me want to ask whether YOU ever get stuck, and whether there are any techniques you use for spotting X-wings, multiple possibles etc.

Hi georgers - I've been wondering the same thing about Animator :o) Also Animator, I've been wondering what the initials underneath your username mean? Can't see them now because I'm writing this lol ... but I think they're MVP.

[simes]

MVP = Most Valuable Professional.
See https://mvp.support.microsoft.com/gp/mvpintro

[joolslee]

Hey thank you for that explanation and link Simes - a well deserved accolade to Animator.

[axis]

Well, I'm just noodling around with this puzzle as well since the problem was posted. Animator, you said look at box 3 to solve it, I'm not sure what technique you are referring to to use to derive a number. Could you explain this please? Thanks.

[joolslee]

Hi Axis, as no one else has come forward yet, I think the technique referred to is explained at http://www.simes.clara.co.uk/programs/sudokutechnique9.htm

[simes]

Axis,

Look at where the numbers 5, 7 and 9 can go in both box 3 and column 8. Then think about the effects on the candidates for other cells in the box and column.

[axis]

Okay, I'm still lost. I understand disjoint subsets but I'm not too sure on reducing candidates from the cells that hold the unique subset. I believe in this puzzles case, the 5,7,9 in block 3 was the triple candidates for the cells r1c8, r2c7, r2c8. However, what confuses me is why this works when r1c8 doesn't hold all three just two of them?

Also, assuming I did understand the above, to work it out gives me a 7 in r8c8 and a 2 in r9c8? Is this the two cells in column 8 I should find? Bear in mind that if it is I didn't figure it out really because I still dont see why the reducing in block 3 works without the 7 in r1c8? Thanks.

[georgers]

Okay, I'm still lost. I understand disjoint subsets but I'm not too sure on reducing candidates from the cells that hold the unique subset. I believe in this puzzles case, the 5,7,9 in block 3 was the triple candidates for the cells r1c8, r2c7, r2c8. However, what confuses me is why this works when r1c8 doesn't hold all three just two of them?

HI!
Failing a response from my elders and betters, let's have a shot at saying how I tackled this:
I actually started with the 1,2,4,8 set because I couldn't, at first, see how the 5,7,9 set worked. There are 4 numerals so 4 locations need to be part of this set --- and further locations with one or more of the constituent numbers can have those numbers deleted. The 4 locations are r1c9, r3c7, r3c8,r3c9. So the other 2's in that square and, crucially, the 8 in r1c8 can all be removed.
That leaves as possibles 5 & 9 in r1c8, and 5,7,9 in r2c7 and r2c8: the grouping Animator was talking about.
After that repeated application of the same concept elsewhere led to the solution.
Hope that helps...