dailysudoku.com

[Chinaman]

The Times Sunday Sudokus are really tough!

Their 'Fiendish' puzzles are usually fun to solve, but all 3 Sunday Times puzzles I gut stuck.

Have a look at the latest:



I can find very fast the '9' R6C7 - and after some more analyzing the '1' in R2C6

But after that I am clueless. I like to add that I don't like to guess.

[hugo]

I tried and couldn't get any further either! Interestingly enough, if you crunch it through the sudoku draw you get this remark:

'This puzzle may not be solvable using simple logic alone. It may require look ahead logic that this tool doesn't understand, or trial and error, or it may have more than one solution, or no legal solution. This tool should clearly be able to tell the difference, but can't right now!'

Might be the time to write to the paper asking for clarification! One wouldn't like to think the sudoku site can't understand the logic employed, or a quality newspaper resorts to something as vulgar as 'trial and error'. I did think it seemed likely that R8C7 would be a 3 (75% chance) so I am going ahead with that for now.
Cheers,
Hugo

[Chinaman]

OK, I got it. But it really was not easy. I had to study the 'hidden subset' technique. http://www.simes.clara.co.uk/programs/sudokutechnique9.htm

If you do that and look at the 3rd collum the numbers left are (after I add the 9 and the 1):

6
78
134789 (=349)
---
178
578
58
----
13479 (=349)
347 (=34)
2

By excluding the last 7 from 347 the only 7 left in R8 will be in C4 (left from the 1).

After that it's simple logic.

[someone_somewhere]

Yup,
That was for the advanced onces.
You got to this level! It's time to learn the "X-Wing".
Get to the previous mentioned link and learn this nice combination.

Than you can apply it for the above position:

1 in r2c6 - Sole Candidate
9 in r6c7 - Unique Horizontal
9 not in r3c2, it is in r3c3 r7c3 r3c6 r7c6 (X-Wing on Row)

see u,