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### (Classic) Sudoku

Posted: **Tue 23 Nov, 2010 11:24 pm**

by **detuned**

Let's get the ball rolling here. Based heavily on the

nikoli wording:
- Place a number from 1 to 9 in each empty cell. (One number per cell.)
- Each row, column and 3x3 box (surrounded by bold outline) should contain each number from 1 to 9.

Sudoku puzzles sometimes come in grids sized 6x6 (using the numbers from 1 to 6); 8x8 (using the numbers from 1 to 8); 10x10 (using the numbers from 1 to 10, or sometimes 0 to 9); 12x12 (using the numbers from 1 to 12, or sometimes 1 to 9 together with A,B,C); 16x16 (using the numbers from 1 to 16, or sometimes 1 to 9 together with the letters from A to G) and 25x25 (using either the numbers from 1 to 25, or the letters from A to Y).

These puzzles use the following sized boxes (surrounded by bold outline) as the third constraint respectively: 3x2, 4x2, 5x2, 4x3, 4x4, 5x5. In all cases, each row, column and box should contain each of the number/letter sets.

### Re: (Classic) Sudoku

Posted: **Wed 24 Nov, 2010 12:59 am**

by **nickdeller**

Reasonable first cut, but it certainly needs to be specified that

*3x3 box* means boxes surrounded by a bold outline. A good rule of thumb in instruction writing is to assume your reader has never, ever seen one of these puzzles before.

For my money, variants which differ only in grid size ought to be covered in this thread rather than individual ones, with almost identical sets of standard instructions tailored to each - I believe 6x6, 9x9, 12x12 and 16x16 are all currently being published by at least one national newspaper, I suspect that 8x8 is as well, and 25x25 isn't unheard of (although in my view, it really SHOULD be!

).

### Re: (Classic) Sudoku

Posted: **Wed 24 Nov, 2010 1:42 am**

by **GarethMoore**

nickdeller wrote:For my money, variants which differ only in grid size ought to be covered in this thread rather than individual ones, with almost identical sets of standard instructions tailored to each

You can define the puzzle more generally by saying

*just* "bold-lined regions" (or some such) instead of specifying the box shapes by dimension. That way you can include all sizes as well as all jigsaw puzzles. Also it allows better for non-square boxes, such as 2x3 versus 3x2 in 6x6 Sudoku.

Generally I would certainly avoid basing anything on the Nikoli instructions. They are often just plain wrong in English, and there is at least one (I forget which) which omits a critical part of the instructions too. However their worked examples are sometimes fun - I'd use them as a supplementary resource, not a primary source for instructions. (at least in English!)

### Re: (Classic) Sudoku

Posted: **Wed 24 Nov, 2010 10:03 am**

by **PuzzleScot**

From WSC 2010 Classics round:

"Place the digits 1 through 9 into the empty cells in the grid (a single digit per

cell) so that each digit appears exactly once in each of the following

regions: the nine rows, the nine columns, and the nine outlined 3×3 regions."

WSC 2009/2008/2006:

"Fill in the grid so that every row, column and 3x3 box contains all the digits from 1 to 9"

WSC 2007:

"Place a digit from 1 to 9 into each of the empty squares so that each digit appears exactly once in each

of the rows, columns and the nine outlined 3x3 regions."

I thought this would be simple

### Re: (Classic) Sudoku

Posted: **Wed 24 Nov, 2010 7:11 pm**

by **ronaldx**

When I'm writing formal instructions, I always imagine that aliens are reading them

For that reason, I would ask them to place one digit into each empty cell

so that each row, each column and each bold-outlined region contains each number from 1 to N "exactly" once.

although even that might be a little ambiguous!!

### Re: (Classic) Sudoku

Posted: **Wed 24 Nov, 2010 8:35 pm**

by **detuned**

It strikes me that the original poster has a lot of power over the rules!

Anyhow, I've updated to allow for different sized puzzles (seems sort of clunky to me, but it does the job). I've stuck with "*a digit from 1 to 9*" rather than "*one digit from 1 to 9*" as the former version is clearly non-plural - the latter mixes up numbers in different contexts.

Adding the caveat that each digit should appear exactly once in each of the constraints is superfluous information - which in my mathematical training has always been considered bad style.

### Re: (Classic) Sudoku

Posted: **Wed 24 Nov, 2010 9:11 pm**

by **nickdeller**

Might be as well to use "number" rather than "digit", neatly solving the problem that 10, 12, 16, 25 et al aren't digits!

### Re: (Classic) Sudoku

Posted: **Fri 26 Nov, 2010 12:18 am**

by **ronaldx**

In the rules as they stand (at the top of the page), there's nothing to prevent me from placing several numbers into one cell (in that I'm not disallowed from doing so)

In fact I could fill up every cell with all of the numbers 1-9 and I've completed the puzzle according to these rules!

At least one use of the word "exactly" ought to be there.

(plus, this illustrates the general need for an easy-to-understand visual example alongside any instructions we give - this, I'd think, is how almost everyone first learned how sudoku really worked)

Adding the caveat that each digit should appear exactly once in each of the constraints is superfluous information - which in my mathematical training has always been considered bad style.

In contrast to mathematics: In my educational training, giving the theoretical minimal set of instructions for people to follow is considered very bad style! The style guide for mathematics understandably asks us to omit unnecessary information, but in puzzling it's highly desirable to make the detail as clear as possible. (or suffer a lengthy Q&A session)

Having said all of that, Sudoku is a special case. My favourite instruction set would be:

"Sudoku...

*you know what to do!*"

### Re: (Classic) Sudoku

Posted: **Sun 28 Nov, 2010 2:14 pm**

by **drsteve**

GarethMoore wrote: You can define the puzzle more generally by saying *just* "bold-lined regions" (or some such) instead of specifying the box shapes by dimension. That way you can include all sizes as well as all jigsaw puzzles. Also it allows better for non-square boxes, such as 2x3 versus 3x2 in 6x6 Sudoku.

I'd avoid grouping Jigsaw/Irregular Sudoku in here, as if there's going to be tips as well, there are extra logical steps with Jigsaw that don't apply to normal - e.g. if in a 9x9 there is a long L-shape (8 cells with a sticky out one) then the sticky out number is the same as the unused cell in the row or column. Apologies for the technical language, but you know what I mean. Hopefully.

### Re: (Classic) Sudoku

Posted: **Sun 28 Nov, 2010 2:26 pm**

by **ronaldx**

drsteve wrote:
I'd avoid grouping Jigsaw/Irregular Sudoku in here, as if there's going to be tips as well, there are extra logical steps with Jigsaw that don't apply to normal - e.g. if in a 9x9 there is a long L-shape (8 cells with a sticky out one) then the sticky out number is the same as the unused cell in the row or column. Apologies for the technical language, but you know what I mean. Hopefully.

Agree totally regarding tips.

However, if we are writing a set of rules for publication, then I prefer Gareth's wording

(even though that also applies to a more general puzzle type)