## NRC 31 december 2005

For fans of Killer Sudoku, Samurai Sudoku and other variants
I tweaked my generator to generate these too. Here is a 14-clue NRC-Style sudoku:

Code: Select all
`. . .|. . .|. . .6 . .|. . .|5 . .8 . .|4 . 9|. . .-----+-----+-----. . .|. . .|. . .. . .|. . .|. . .. . .|7 . .|. . .-----+-----+-----. . .|. 1 .|7 . 69 . .|. . .|2 . .3 2 .|. . .|. 8 .`

I also tested these and wrote a little solving guide appendix:

NRC-Sudoku extra solving techniques.

The NRC-Sudoku has 4 additional AllDifferent constraints in 3x3 regions at rows 234 & 678 and colums 234 & 678.
I will call these the NRC-Boxes.

Intersection removals

When all candidates for digit d in a row or column are members of an NRC-Box, the remaining candidates for digit d can be eliminated from that NRC-Box.
When all candidates for digit d in an NRC-Box are members of a single row or column, the remaining candidates for digit d can be eliminated from that row or column.

When all candidates for digit d in a Box are members of an NRC-Box, the remaining candidates for digit d can be eliminated from that NRC-Box.
When all candidates for digit d in an NRC-Box are members of a single Box, the remaining candidates for digit d can be eliminated from that Box.

Disjoint subsets

All normal subset rules also apply to the NRC boxes.

NRC-Wing

When all candidates in 2 NRC-Boxes for digit d are located in exactly 2 rows or columns, the remaining candidates for digit d can be eliminated from those 2 rows or columns.

X-chains and coloring

Conjugate pairs can also be found in the NRC-Boxes.

Happy solving.

Ruud.
Ruud

Posts: 664
Joined: 28 October 2005

One way to view these is as a vanilla/killer mix, i.e. the four extra constraints are 45/9 cages.
HATMAN

Posts: 214
Joined: 25 February 2006

I was playing around with these puzzles a little more when I suddenly realized that there are 4 more AllDifferent constraints in these NRC sudokus.

Look at this picture:

Code: Select all
`. g g|g . h|h h . e a a|a e b|b b e e a a|a e b|b b e -----+-----+----- e a a|a e b|b b e . g g|g . h|h h . f c c|c f d|d d f -----+-----+----- f c c|c f d|d d f f c c|c f d|d d f . g g|g . h|h h .`

I marked the NRC-Boxes a-d. However, the regions I marked e-h also must contain digits 1 through 9, simply because they complete the 3 rows/columns containing 2 NRC-Boxes.

This gives us a few extra solving techniques:

- Hidden singles for regions e-h
- Disjoint subsets for regions e-h
- Conjugate pairs in region e-h
- The NRC-Wing in my previous post is actually a block-block interaction. These can also be expanded to include the e-h regions.

Ruud.
Ruud

Posts: 664
Joined: 28 October 2005

But the remaining 9 cells r159c159 (call it region i) must also contain digits 1-9... (I'm sure you're aware of it already...) So it's just another variant having 9 extra groups of 9 cells... kind of like the disjoint group variant...

What bugs me is what does NRC stand for? Is it just the name of a Dutch newspaper? Can we find a better name for this class of puzzles? Or at least associate something more meaningful with the 3 letters (e.g. Naughty Rude Cracker sudoku... like that's a better name! )
udosuk

Posts: 2698
Joined: 17 July 2005

Good observation, region i.

It can indeed be used for hidden singles, disjoint subsets, and conjugate pairs, but I cannot see any useful interactions with other regions.

NRC = Nieuwe Rotterdamse Courant (indeed the name of a Dutch newspaper).

After our discoveries, how about: No Real Challenge?

Ruud.
Ruud

Posts: 664
Joined: 28 October 2005

Ruud wrote:I cannot see any useful interactions with other regions.

I have to correct myself here. I found a few of these that can be advanced with intersection removal between a line and the i region.

As for a better name: WinDoKu. The poor puzzle resembles the Windows logo with the 4 extra boxes in a different color.

Ruud.
Ruud

Posts: 664
Joined: 28 October 2005

WinDoKu

Very thoughtful name!

It's just irritating to have any remote association between sudoku and Mr. Gates' multi-trillion franchise...
udosuk

Posts: 2698
Joined: 17 July 2005

Ruud wrote:No Real Challenge?
Ruud.

That depends on the difficulty of puzzles you generate in this variant.
Your solving guide appendix looks very promising!
evert

Posts: 186
Joined: 26 August 2005

As of version 1.5.0, Sudocue handles Windoku (NRC) puzzles.

Hoe Heet Het is a Dutch site that has many NRC puzzles.
tso

Posts: 798
Joined: 22 June 2005

Hi,
Just testing my program if it can deal with this kind of puzzle.
Could somebody confirm that, in order to solve this puzzle, I really need a naked or hidden n-tuple
with such a new group involved?
Code: Select all
`009060000002000400003008001200500009000001000000000003000400090000000000008000000`
evert

Posts: 186
Joined: 26 August 2005

I did it with naked and hidden singles and pairs, locked numbers and one naked triplet - the triplet was probably not necessary. All in all it was a straightforward WinDoku, this is the first vanilla I’ve done in ages.

Not fully clear on your question so I tried it again: started with hidden and naked singles in windows as well as r c n, then naked pairs in windows locked numbers, hidden pairs then hidden singles and naked singles to finish. So nothing more than singles and doubles with single number locks but I used the windows fully. Later I'll see if I can do it just using the windows for singles.
HATMAN

Posts: 214
Joined: 25 February 2006

Evert

I cannot avoid using the 67 doublet at r67c6 in W4 and a hidden pair 47 at r19c2 in hidden group r159c234. It needs some big vanilla (XY chains) but otherwise the windows were only used for hidden or naked singles. I hope that this answers your question.

Maurice
HATMAN

Posts: 214
Joined: 25 February 2006

Thanks for looking at it!

It's just that the puzzle was generated by the lates version of my program, and one version earlier couldn't solve it. The newest version had naked and hidden n-tuples implemented specifically for the new windows.
I think it works ok but I wanted some confirmation.
evert

Posts: 186
Joined: 26 August 2005

Evert

You might wish to try your solver on this "Both Windows" one I posted on Ruud's site:

http://www.sudocue.net/forum/viewtopic.php?t=887

Maurice
HATMAN

Posts: 214
Joined: 25 February 2006

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