The New Sudoku Players' Forum

[alanh]

I'm currently stuck at:

31-|-47|--6
--6|-3-|1-7
87-|691|-53

-5-|-23|679
7-3|916|5--
69-|75-|-31

-3-|16-|7-5
--7|-8-|3--
2--|37-|---

I've found the X-Wing (2) in rows 3,6 columns 3,7 which has eliminated the 2 from r1c7

Can see no other X-Wings or triples from here.
Thanks
Alan

[Karyobin]

There are two Hidden Pairs, one in Box 7 and one in Box 9. When you find them, that only leaves one place for a '9' in Row 8.

After that, look for a few Candidates Locked in a Row set-ups and you're there.

[alanh]

Thanks
I'm not sure if the X-Wing actually helps.
Having said I can see no triples, I think there is one in Column 8 (289) which places the 4 in r5c8.
From there it solved quite easily, but I'd hate to think it was just a lucky guess!

Alan

[Karyobin]

The X-wing does help, and I'll explain why.

There is no Naked Triple {2,8,9} in Column 8. There is a Naked Quad {2,4,8,9}, but this only serves to identify the Hidden Pair {1,6} in that column. By identifting the Hidden Pair {1,5} in Box 7, you lock the 9's in Row 7 into that box. From this you can exclude the 9 as a candidate from r7c6 and r7c8, leaving the remaining two 9's having to be in r9c7 and r8c6.

Remember the X-wing? That allowed you to remove a candidate 2 from r1c7. Now, the 9 you just placed in r9c7 allows you to do the same with the candidate 9, leaving r1c7 to be 8.

The next step was to find candidate 8's locked in a row in Box 6, allowing you to remove a candidate 8 from r5c2, resulting in a Hidden Pair {2,4} in Column 2. See the 6?

The rest, as people round here have started saying, is trivial.

[alanh]

Cheers karyobin
This is beyond my Sudoku skills (as yet)
But thanks for the insights
Until I saw these forums I hadn't worked out X wings...still working on the swordfish!

[Karyobin]

One final hint: I have never used a swordfish. Puzzles exist that do require them, but in my experience they are few and far between.

[emm]

I always look for swordfish. Because they are few, it's really cool to find one!

[bridgarw]

What is a "swordfish"? I have figured out "X wing" at last (thanks Alan for your very specific post) and managed to complete the Sunday superior after that.

I have never knowlingly used the swordfish technique, despite having completed almost all the fiendish puzzles (except for a couple of the earlier ones).

[Shazbot]

These two sites have excellent explanations, along with diagrams, to explain both of these techniques and more.

http://www.angusj.com/sudoku/hints.php
http://www.simes.clara.co.uk/programs/sudokutechniques.htm

[b00sfuk]

Could somebody with Sundays paper do a quick check for me please and confirm that the one published does match the one now posted to the Times website at http://www.timesonline.co.uk/article/0,,2092-1793864,00.html

I'm totally stumped, I finally loaded it into the software I've just downloaded from angusj's website and it says it is asymmetrical with multiple solutions; I am hoping it has been mis-transcribed and it is not me!

cheers

[PaulIQ164]

Yeah, that one on the website is certainly asymmetrical, and has multiple solutions at least according to the Susser. Odd, since Pappocom's program specifically doesn't generate asymms.

[b00sfuk]

Could somebody with Sundays paper do a quick check for me please and confirm that the one published does match the one now posted to the Times website

The Times has now posted a revised grid that has some more numbers filled in. I'm optimistic my sanity will return now I know it was not me!