I'm looking for strategies, tactics and tips on playing Sudoku.  In
addition, I'm looking for the best resources on the web for the game 
Any
information about the history of the Sudoku game as well would be
great.  

In addition any affliate site information for the game of Sudoku would
be very welcomed.

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Request for Question Clarification by websearcher-ga on 23 Jul 2005 09:52 PDT

A couple of tricks I use to get started on a Sudoku puzzle:

1. Check each horizontal set of three 3x3 boxes. If exactly two of the
3x3 boxes in a horizontal set contain the same number, then it is
often easy to figure out where that number goes in the third box (by
simple process of elimination).

2. Do the equivalent trick for each vertical set of 3x3 boxes. 

3. If any squares have been filled in in step 2, go back to step 1 and
repeat. If not, go to step 4.

4. Go the row, column, or 3x3 box that has the most squares filled in
and see whether any of the "missing" numbers/squares can be filled in.
Do the same for other rows, columns, 3x3 boxes that have many squares
filled in as well.

5. If any squares have been filled in in step 4, go back to step 1 and
repeat. If not, go to step 6.

6. At this point take a light pencil and for every unfilled square,
write in all the numbers that could possibly go in that square. (I use
the corners of the square to put the numbers.)

At this point there are several other logic-based tricks I use to
eliminate possibilities and determine final values for squares. If you
can follow the above steps - and they work for you - I'd be willing to
provide these other logic steps as the official answer to this
question.

Let me know. 

websearcher

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Clarification of Question by tvilfr-ga on 23 Jul 2005 17:36 PDT

Yes can follow that so far.  Also, as the question says, I'm also
looking for resources, etc as well.

Thanks
p.s. why are other people allowed to comment ?  If I'm paying for this
service, you would expect some privacy and not some lame comments like
some of them are.

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Request for Question Clarification by websearcher-ga on 23 Jul 2005 20:54 PDT

Hi tvilfr:

I'm glad you can follow my suggestions so far. I've been solving
Soduko puzzles for a while, but I've never actually written down my
method before.

I'll complete the rest of my strategy for you tomorrow. 

As for your question about non-researchers being able to
comment....it's true that anyone visiting the Google Answers site
(assuming they sign up for an ID) can make comments, but only
qualified Google Answers Researchers (GARs) can post Answers or make
clarification requests. Only a posted Answer actually costs you
anything. You can tell a GAR by the fact that their names are linked.

It's true that sometimes comments left by non-researchers are not very
helpful - but on the other hand sometimes they have proven to very
helpful as well. You can always choose to ignore them. I'm not 100%
sure why Google decided to include the ability for non-researchers to
make comments, but it's likely they wanted to promote a more "open"
system.

websearcher

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Request for Question Clarification by websearcher-ga on 23 Jul 2005 20:55 PDT

P.S. I'll also find those resources you want.

Hi tvilfr:

OK, let's go back to step 6 from above:

6. At this point take a light pencil and for every unfilled square,
write in all the numbers that could possibly go in that square. (I use
the corners of the square to put the numbers in a small size.)

You have to be *very careful* doing this step. Each unfilled square
must have written in it (in pencil) each number that has NOT currently
been eliminated for that square. The goal from here is, through a few
logic steps, to eliminate these written (in pencil) possibilities
until squares that only have one possibility are left.

7. Check each row, column and 3x3 box for a match which is a
combination of n unfilled squares that have between them only n
possible number values. For example, if you have two unfilled squares
in a row both of whose only possible values were 4&6, then you've got
a match. Another example: if you've got three unfilled squares in a
3x3 box which contain just the possible values 2&7&9, 2&9, and 7&9
respectively, then you've got a match. When you have a match, every
other unfilled square in that particular row, column or 3x3 box can
have the numbers you found in the matched boxes eliminated (by
erasing). For example, in the first example above, if another square
in the candidate row has possible values 2&4&8, then you erase the 4
from that box, leaving 2&8. [Important note: If the match you find is
*simultaneously* in a 3x3 box as well as in a row or column, then you
can perform the elimination step on *both* structures.]

8. Once you've found a match and done the appropriate elimination(s)
from other boxes, *if* you've gotten to the point where an unfilled
box now has only one remaining possibility, fill in that number in pen
(in a similar character size to the pre-filled numbers). Go to step 7
and repeat. [Hint: it is often quicker to examine the rows, columns
and 3x3 boxes that have been effected by recent possibility
eliminations. You are more likely to find another match there.]

9. Most puzzles can be completely solved by applying steps 7 & 8 over
and over again. However, I have found that occasionally you need a
further step that is a variant on step 7. Check each row, column and
3x3 box for a match which is a combination of n unfilled squares that
share between them n number values where those n numbers are *not
found anywhere else* in that particular row, column or 3x3 box. For
example, if you have a column with 5 unfilled boxes whose possible
values are 2&3&4, 2&6&9, 6&9, 3&4&6&9, 2&6&9, then you've got a match
on the first and fourth square, both of which have 3&4 and those two
numbers are not found anywhere else in that column. When you get a
match like this you can eliminate *from the matching squares* any
other possible values. (In this case, you'd end up with: 3&4, 2&6&9,
6&9, 3&4, 2&6&9.) Go to step #8.

That's it! So far, I've been able to solve every Sudoku puzzle I've
tried by applying these steps - so long as I don't make any mistakes
in the application!

I'll work on the resources next and post them in a clarification. 

websearcher

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Clarification of Answer by websearcher-ga on 24 Jul 2005 20:15 PDT

Hi tvilfr:

Here are the best-of-the-best for Sudoku resources on the Web:

Sudoku
URL: http://en.wikipedia.org/wiki/Sudoku
Note: By far, the best explanation, history, and list of resources for
Sudoku I've seen.  A must read!

su|do|ku
URL: http://www.sudoku.com/
Note: sample puzzles, rules, tips, forums, etc. 

Solving Sudoku
URL: http://www.sudoku.org.uk/PDF/Solving_Sudoku.pdf
Note: An EXCELLENT guide to solving Sudoku puzzles!

Online Su Doku speed challenge
URL: http://www.sudokufun.com/
Note: Pit your solving speed against others!

Web Sudoku
URL: http://www.websudoku.com/
Note: Billions of potential puzlles, solvable online

Sudoku Solver
URL: http://www.sudokusolver.co.uk/
Note: Enter a puzzle and it tries to solve it for you - with list of
steps taken for illustration!

Sudoku Books
URL: http://www.amazon.com/exec/obidos/search-handle-url/ref=pd_kk_sr_1/102-0914191-8762554?index=stripbooks&field-keywords=sudoku%20puzzles

I was unable to find any Sudoku-specific affiliate information. 

Search Strategy (on Google):
* sudoku
* "sudoku software" 
* "sudoku solver" 
* "sudoku history" 
* "history of sudoku"
* "sudoku books" 
* affiliate sudoku

websearcher 

I hope this helps.

I was hoping for more fill in regards to the answer.   But still do
not understand Google's intent of letting "tirekickers" being able to
comment on questions when a person is asking and paying for such
service.

I was hoping for more "bang" for the buck since I have seen others get
quite a bit of information.

For a very comprehensive article on the game, check out the following
from Wikipedia:

http://en.wikipedia.org/wiki/Sudoku

You can download a software version of the game from www.sudoku.com
(available on a 28-day free trial).

This contains numerous tips on how to play the game. Highly
recommended. I've hardly stopped playing it for a week!

ITS DOING MY HEAD IN. One of the tricks to it is to start in the
centre box and apply each number in turn to only that box. By checking
the numbers across and up and down of all nine lines. When all
possible results are completed for the centre box, do the same on
boxes 1-9. If no options possible on , say No. 2, go to No. 3 box  
/.../.../...
                     /.../.../...
                     /.../.../...
                     /.../.../... ITS DOING MY HEAD IN...AND SO ON.

Dear tvilfr-ga,

The present rage of "Sudoku" is all over the world!

Is it not funny how a game invented by a great Europian mathematician,
has been made their own by the ingenious Japaneese!

kudos to their own brand of genious!

Hope you do remember how the "ZD "(Zero defect) concept invented by an
American is adopted by Japaneese and made their National creed to beat
America at their own game!

Now how I solve the game step by step.

the priliminary steps are what I call as "donkey steps" which dont need much logic:

1.Tranfer  the paper puzzle to an MS excel sheet.
2. there are only three things to solve the puzzle.
3. the horizotal lines, the vertical lines and the nine squares which
make up the puzzle.
4. note on the  side of each column and row the missing numbers from
that row or column.
5. now the " donkey work' is over.

6. now examine each separate smaller square and crossd out only the
numbers which are common to both the row and column in that square.
7. now examine each of the smaller squares.
8. cut out those numbers which already appear on the smaller square.
9. Most probably you would have found already, independent numbers in
some of the individual squares.

10.True logic starts from here.
11. check which columns or rows have the maximum numbers already in place.
12. Try and fill them up first.
13. then proceed to the other rows and columns and fill in the numbers.

14.the method descibed may look cumbersome. But it is logcal.
 
By the way I and my wife are addicts from India of this game. We take
about half an hour max. to solve any Sudoku puzzle.

regards, 

ivlnchary

There are free games available here:

http://www.websudoku.com

They're automatically generated (I assume), so there are billions
available, the site lets you print them out or solve online, and you
can select degree of difficulty.

As far as tactics, I think the wiki article has a good summary of the
major strategies. But I think the best way is just through practice
and logical deduction.

tvilfr,

Don't worry - I shan't come anywhere near your tires in future. Nor,
I'm sure will any of the other altruistic individuals who were merely
trying to help.

Personally, I think that websearcher delivered a pretty impressive
'bang' for your buck.