## Sudoku World Cup - The Times Brain Teasers

For fans of Killer Sudoku, Samurai Sudoku and other variants

### Sudoku World Cup - The Times Brain Teasers

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   323 5  13 | 4  12 8  | 9  6   78  6  9  | 7  5  3  | 2  4   1---------+----------+---------5  9  2  | 8  4  7  | 13 13  67  8  6  | 1  3  5  | 4  9   21  3  4  | 2  6  9  | 8  7   5---------+----------+---------6  12 5  | 3  8  4  | 7  12  99  4  13 | 5  7  12 | 6  123 823 7  8  | 9  12 6  | 13 5   4---------+----------+---------`
Crazy Girl

Posts: 189
Joined: 08 November 2005

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 ?
afjt

Posts: 82
Joined: 07 September 2005

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?
vidarino

Posts: 295
Joined: 02 January 2006

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
Crazy Girl

Posts: 189
Joined: 08 November 2005

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.
vidarino

Posts: 295
Joined: 02 January 2006

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).....

Tarek

tarek

Posts: 2737
Joined: 05 January 2006

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.
PaulIQ164

Posts: 533
Joined: 16 July 2005

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.
Bigtone53

Posts: 413
Joined: 19 September 2005

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.
afjt

Posts: 82
Joined: 07 September 2005

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
Crazy Girl

Posts: 189
Joined: 08 November 2005

The puzzles are meant to be available online here

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

grumpyoldman

Posts: 7
Joined: 08 June 2005

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!!
CathyW

Posts: 316
Joined: 20 June 2005

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     | *-----------------------------------------------------------*`
CathyW

Posts: 316
Joined: 20 June 2005