Guess with pencil marks? (Sunday Times #16 (2005.Nov.13))

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Guess with pencil marks? (Sunday Times #16 (2005.Nov.13))

Postby confucious » Sun Nov 13, 2005 11:15 pm

Today's Superior Sudoku in the Times (13/11/05) I could not solve, even with pencil marks, by logic alone.

I got to the point where I could not find a logical next step and I phoned a friend who had exactly the same numbers in and exactly the same pencil marks as me but she too was stuck.

In the end we resorted to trying one of the numbers in a cell with only two numbers in then working through until we got stuck. Then trying the other number worked through to a completed solution.

Is today's Superior solvable by logic alone? Are we both missing something?
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Postby Crazy Girl » Sun Nov 13, 2005 11:40 pm

Today's Superior Sudoku can be solved with logic alone, a property of all pappocom puzzles.

It takes a lot of tricks to solve this puzzle, if you are not used to solving difficult puzzles take a look at

http://www.angusj.com/sudoku/hints.php

pay particular attention to the Swordfish section, this is the first trick you need to use.

also worth a look are hidden pairs and x-wings.

post your puzzle where you are stuck if you need more help.

edit: there is a swordfish in this puzzle, but it can be solved with just using a x-wing

... try looking at the lucky number 7 ! !
Last edited by Crazy Girl on Sun Nov 13, 2005 7:55 pm, edited 1 time in total.
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Postby PaulIQ164 » Sun Nov 13, 2005 11:41 pm

It should be doable. The most likely thing you're missing (though I haven't looked at this particular puzzle) is what's called an "X-Wing". It's a tad complicated, but if you do a Google search for "Sudoku X-Wing" or something I'm sure there are websites that can explain them (maybe someone else has the URLs?).

Edit: darn, beaten to it. Although you should never need a Swordfish for a Pappocom puzzle. The only tactic you need in Sunday ones that you never need in weekday puzzles is the X-Wing.
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can be solved with X-Wing

Postby aleph » Mon Nov 14, 2005 8:03 am

I solved it using 2 X-Wings

It is a really interesting one.
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Postby Bigtone53 » Mon Nov 14, 2005 11:58 am

I solved it using 2 X-Wings

It is a really interesting one.


Yes, 2 x-wings did it for me. As Crazy Girl says, one of them involved 7s but I needed another one before then.
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Postby dalek » Mon Nov 14, 2005 1:57 pm

I solved this one quite quickly and wasn't aware of using X wings (although that doesn't mean I didn't......).:)
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Postby Heuresement » Tue Nov 15, 2005 9:54 am

As previously remarked this one certainly was interesting.

It was a real pleasure to be able to use a swordfish on this one, as I rarely have the experience. From the other comments, I know that using a swordfish was not necessary, but that doesn't lessen the fun of applying it to this puzzle, and may have contributed to helping me to solve it quicker.

IMO these patterns were easier to see in this puzzle than usual, because there were relatively few empty squares, with only a few candidates.

I hope that the next one is as interesting:)
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Postby confucious » Sun Nov 20, 2005 9:29 pm

Many thanks for all your help and advise - I have a lot to learn.

This weeks didn't even need pencil marks!
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re: The Sunday Times #16 (2005.Nov.13)

Postby Pat » Tue Nov 22, 2005 11:27 am

aleph wrote:I solved it using 2 X-Wings

It is a really interesting one.
Bigtone53 wrote: Yes, 2 x-wings did it for me. As Crazy Girl says, one of them involved 7s but I needed another one before then.

there are indeed 2 X-wings available, but Crazy Girl is right -
only one is needed, the other one is a red herring.

- Pat
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