Sudoku World Cup - The Times Brain Teasers

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Sudoku World Cup - The Times Brain Teasers

Postby Crazy Girl » Mon Mar 06, 2006 1:11 pm

In today's Times there are 4 examples of Sudoku Variants, like what contestants might face at the Sudoku championships in Lucca Italy.

for the variant with conditions:-
Squares with circles must have numbers 1, 2, 3
Squares with squares must have numbers 4, 5, 6
and empty squares must have numbers 7, 8, 9.

Filled in below are numbers 4, 5, 6, 7, 8, & 9. but how do you determine where numbers 1, 2, and 3 go without resorting to advanced techniques.

Code: Select all
---------+----------+---------
4  12 7  | 6  9  12 | 5  8   3
23 5  13 | 4  12 8  | 9  6   7
8  6  9  | 7  5  3  | 2  4   1
---------+----------+---------
5  9  2  | 8  4  7  | 13 13  6
7  8  6  | 1  3  5  | 4  9   2
1  3  4  | 2  6  9  | 8  7   5
---------+----------+---------
6  12 5  | 3  8  4  | 7  12  9
9  4  13 | 5  7  12 | 6  123 8
23 7  8  | 9  12 6  | 13 5   4
---------+----------+---------
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Postby afjt » Mon Mar 06, 2006 1:33 pm

I don't think you can.
I did the last bit by T&E, but I suspect that using colouring (with a 'u' !) would probably work.
I notice though that all the unknowns have 2 candidates, except for r8c8 which has 3. Is this the key to finding a logical solution ?
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Postby vidarino » Mon Mar 06, 2006 1:40 pm

afjt wrote:I notice though that all the unknowns have 2 candidates, except for r8c8 which has 3. Is this the key to finding a logical solution ?


Yep. There is the BUG+1 rule (one polyvalue cell in R8C8 and the rest bivalue). The 1s occur three times in each row, column and box, hence R8C8=1. I don't know if this counts as "advanced", but it's pretty simple to use, IMHO.:) Not particularly known outside this forum, though.

And there's also an XY-Wing at R8C3 (wings R8C6 and R9C1, which eliminates 2 from R9C5), but that probably counts as an advanced technique?
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Postby Crazy Girl » Mon Mar 06, 2006 1:49 pm

I agree we have a BUG/BUG+1 grid and in order to solve it, one has to set R8C8 to 1.

The only thing I don't like about this is, that The Times never needs advanced techniques, like BUG to solve any puzzle, unless they have left off one of the clues to this grid, it looks like a BUG is the only way to solve the puzzle for now.

We will just have to wait and see what The Times publishes tomorrow, when this puzzle should be online:!:
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Postby vidarino » Mon Mar 06, 2006 2:00 pm

Yep, colouring the 1s also takes care of it, but that's definitely an "advanced" technique, by newspaper standards.

Code: Select all
 . a . | . . A | . . .
 . . A | . a . | . . .
 . . . | . . . | . . .
-------+-------+------
 . . . | . . . | A a .
 . . . | . . . | . . .
 . . . | . . . | . . .
-------+-------+------
 . A . | . . . | . a .
 . . a | . . a | . 1 .
 . . . | . A . | a . .


Crashing 'a's all over the place.:)
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Postby tarek » Mon Mar 06, 2006 2:05 pm

There are no easy techniques for this at all...........

We could kill 1 in r8c3 with a finned x-wing (something which we can achieve with other advanced tecniques including simple colouring).....

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Postby PaulIQ164 » Mon Mar 06, 2006 5:05 pm

That's a poor show for competition puzzles. If the methods needed to solve them are more time-consuming than using T&E (as I assume to be the case here) then the puzzle isn't much use for a timed challenge.
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Postby Bigtone53 » Mon Mar 06, 2006 5:33 pm

One of the other 4 examples had 'blocks of 9' of different shapes, which was interesting and involved new thought processes.

I wouldn't hold your breath waiting for these examples to be published tomorrow though, as they have given the answers today.
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Postby afjt » Mon Mar 06, 2006 5:37 pm

Bigtone53 wrote:One of the other 4 examples had 'blocks of 9' of different shapes, which was interesting and involved new thought processes.


If you like these puzzles, there is an archive full of them at http://www.dailysudoku.co.uk/sudoku/index.shtml
The site calls them 'squiggly'. I have seen them referred to as 'jigsaw' elsewhere.
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Postby Crazy Girl » Tue Mar 07, 2006 12:30 pm

Bigtone53 wrote:I wouldn't hold your breath waiting for these examples to be published tomorrow though, as they have given the answers today.


I thought they might publish the puzzles on the web, for the people in Australia/US/... to try, but i can't find the page on their website. If it's published on the web it should have any clues missed in the newspaper version (if there has been any clues missed) and therefore be more accurate.

Also has anyone solved the odd/even puzzle, I have solved all the odd numbers, but there are less clues for the even numbers and I'm currently hitting a brick wall:!::!:
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Postby grumpyoldman » Tue Mar 07, 2006 5:50 pm

The puzzles are meant to be available online here

http://www.timesonline.co.uk/article/0,,2-2071967,00.html

but are unfortunately unreadable
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Postby CathyW » Tue Mar 07, 2006 6:47 pm

There's a pdf of the puzzles here: http://wpc.puzzles.com/sudoku/WSC_sample.pdf

Don't look too closely at page 1 as it's the front and back cover and the back cover has the solutions!!
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Postby CathyW » Tue Mar 07, 2006 10:47 pm

Has anyone tried the odd/even puzzle?

The odd numbers are no problem but I've had to use multiple colouring just to reach this stage. Now I'm really stuck! I think in a competition you'd have to resort to guessing and hoping it worked out.

Code: Select all
 
 *-----------------------------------------------------------*
 | 246   246   1     | 26    8     3     | 5     7     9     |
 | 3     5     26    | 1     7     9     | 4     28    268   |
 | 7     8     9     | 246   5     246   | 1     3     26    |
 |-------------------+-------------------+-------------------|
 | 1     9     3     | 5     24    248   | 7     6     248   |
 | 5     246   268   | 2468  9     7     | 28    1     3     |
 | 246   7     268   | 3     1     2468  | 9     5     248   |
 |-------------------+-------------------+-------------------|
 | 9     26    4     | 7     3     5     | 268   28    1     |
 | 268   3     5     | 248   24    1     | 26    9     7     |
 | 28    1     7     | 9     6     28    | 3     4     5     |
 *-----------------------------------------------------------*
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