The New Sudoku Players' Forum

[evert]

Right now working hard on this puzzle:

Code: Select all

 *-----------*
 |..2|...|...|
 |..4|.8.|9..|
 |...|3..|...|
 |---+---+---|
 |...|..5|4.1|
 |...|...|...|
 |5..|2..|..8|
 |---+---+---|
 |...|..6|.7.|
 |.5.|...|...|
 |...|.3.|.1.|
 *-----------*


(NRC 31 december P. Ritmeester)

Additional information:
The "boxes" R2C2-R4C4 / R2C6-R4C8 / R6C2-R8C4 / R6C6-R8C8
should also contain the numbers 1-9:

Code: Select all

 *-----------*
 |...|...|...|
 |.XX|X.X|XX.|
 |.XX|X.X|XX.|
 |---+---+---|
 |.XX|X.X|XX.|
 |...|...|...|
 |.XX|X.X|XX.|
 |---+---+---|
 |.XX|X.X|XX.|
 |.XX|X.X|XX.|
 |...|...|...|
 *-----------*


Any hints? I'm not really making progress.

[Shazbot]

I get a "too many solutions to count" message from Simple Sudoku with this puzzle.

[Lardarse]

Shazbot, there are 4 extra groups in this puzzle.

Code: Select all

*-----------*
|...|...|...|
|.AA|A.B|BB.|
|.AA|A.B|BB.|
|---+---+---|
|.AA|A.B|BB.|
|...|...|...|
|.CC|C.D|DD.|
|---+---+---|
|.CC|C.D|DD.|
|.CC|C.D|DD.|
|...|...|...|
*-----------*

[ChrisT]

That’s a really fun puzzle! It’s very satisfying to be able to fill in the grid based on so little starting information. I’ve come to a solution after some very careful candidate management. You only need to apply the same rules as you would use on a normal sudoku, but making sure you apply them in relation to the four extra boxes at every stage. These hints might help:

Code: Select all

*-----------*
 |...|...|...|
 |.A5|A.B|BB.|
 |.AA|*.B|BB.|
 |---+---+---|
 |.*A|*.B|BB.|
 |...|...|...|
 |.CC|C.D|DD.|
 |---+---+---|
 |.CC|C.D|DD.|
 |.CC|C.D|DD.|
 |...|...|...|
 *-----------*

Keep your candidates up to date, using all the information available. If you have placed a 5 as shown above, as well as the usual eliminations you can remove the candidate 5 from the cells marked with asterisks

Code: Select all

*-----------*
 |...|...|...|
 |.AA|A.B|BB.|
 |.AA|A.B|BB.|
 |---+---+---|
 |.AA|A.B|B55|
 |...|...|...|
 |.CC|C.D|DD.|
 |---+---+---|
 |.CC|C.D|DD.|
 |.CC|C.D|DD.|
 |...|...|.55|
 *-----------*

Watch out for singles within the extra four boxes. In the above configuration, if the cells marked are the only remaining options for the number 5, we know that 5 must go in r4c8 to satisfy box B. In normal sudoku we would not be able to place the 5s at this point.

Code: Select all

*-----------*
 |...|...|...|
 |.A*|A.B|BB.|
 |.A*|A.B|BB.|
 |---+---+---|
 |.5A|5.B|BB.|
 |...|...|...|
 |.CC|C.D|DD.|
 |---+---+---|
 |.CC|C.D|DD.|
 |.CC|C.D|DD.|
 |...|...|...|
 *-----------*

Make use of box/line interactions that involve the extra four boxes. In the above example, if places marked “5” are the only cells in row 4 with candidate 5, you can remove candidate 5 from the cells marked *

Code: Select all

*-----------*
 |...|...|...|
 |.AA|A.B|BB.|
 |.AA|A.B|BB.|
 |---+---+---|
 |*5A|5**|***|
 |...|...|...|
 |.CC|C.D|DD.|
 |---+---+---|
 |.CC|C.D|DD.|
 |.CC|C.D|DD.|
 |...|...|...|
 *-----------*

Conversely, if the marked cells are the only cells in block “A” with candidate 5, then all the marked eliminations can be made.

I hope at least some of that makes sense! It's not easy to explain some things when the language of sudoku doesn't quite cater for this type of puzzle... Let me know if some of it needs clarifying.

Has anyone seen this type of puzzle elsewhere? I'd be very interested in seeing some more of them!

Chris

[evert]

Has anyone seen this type of puzzle elsewhere? I'd be very interested in seeing some more of them!

The Dutch newspaper NRC Handelsblad each saturday.
It's also fun we start with 16 clues where for normal sudoku no 16-clue puzzle is known yet.
BTW I myself messed the puzzle up found two 8's in one row.

[evert]

I found this one easier

Code: Select all

100000000
029000400
000008200
000800000
000020900
007900008
000010300
005400060
000000000


[ChrisT]

Thanks for posting another, evert! I enjoyed having a try at a second one.

Chris

[evert]

Do you have a solution of the 1st?
During my second attempt I found a contradiction again.

[ChrisT]

This is what I got.

Code: Select all

+-------+-------+-------+
| 8 3 2 | 1 5 9 | 7 4 6 |
| 7 1 4 | 6 8 2 | 9 3 5 |
| 6 9 5 | 3 4 7 | 1 8 2 |
+-------+-------+-------+
| 3 2 8 | 7 9 5 | 4 6 1 |
| 4 6 9 | 8 1 3 | 2 5 7 |
| 5 7 1 | 2 6 4 | 3 9 8 |
+-------+-------+-------+
| 1 8 3 | 9 2 6 | 5 7 4 |
| 9 5 6 | 4 7 1 | 8 2 3 |
| 2 4 7 | 5 3 8 | 6 1 9 |
+-------+-------+-------+

Chris

[MCC]

Once I got myself into the mindset of using a fourth constraint all that I needed were singles and naked pairs.

MCC

[evert]

Before some forum problems a member compared this to vanilla
and killer sudoku.
My question is what's vanilla sudoku?
Couldn't really find an example by Google...

[udosuk]

"Vanilla sudoku" means your plain, simple, boring numbered sudoku with 17 or more clues (until somebody find that elusive 16-clue unique-solution sudoku puzzle). That means no cages, no extra restriction, but only one solution, as opposed to killer sudoku or other variants. Example: what the Times currently publishes each day with rating as Easy/Mild/Difficult/Fiendish/Superior...

It is probably originated from the www.djape.net forums...

[Red Ed]

Just a quick note in passing that Andries Brouwer recently calculated that there are 6337174388428800 ways to make a valid NRC Sudoku grid, and I have confirmed this number. I did this by breaking the work up into a "gang of 21024" (cf. "gang of 44" for vanilla sudoku) representatives of band 1, then brute-force counting from there. Many of the per-band-rep counts were the same (in fact 11666 of them were zero), so it seems very likely that there's a more efficient algorithm to do the count involving a smaller "gang" of band 1 representatives.

[aeb]

Has anyone seen this type of puzzle elsewhere? I'd be very interested in seeing some more of them!

The Dutch newspaper NRC Handelsblad each saturday.
It's also fun we start with 16 clues where for normal sudoku no 16-clue puzzle is known yet.

Here is an 11-clue one.

Code: Select all

.........
.1......3
.....8...
.....9.4.
.6.......
..5......
8.43.....
.......2.
.........


Now these NRC Sudokus also appear daily in nrc.next.

[evert]

How exactly did you create the 11 clue?
In nrc.next they seem to be easier.