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.

Request for Question Clarification bywebsearcher-gaA couple of tricks I use to get started on a Sudoku puzzle:

1. Check each horizontal set of three 3×3 boxes. If exactly two of the

3×3 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 3×3 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 3×3 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, 3×3 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

Clarification of Question bytvilfr-gaYes 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.

Request for Question Clarification bywebsearcher-gaHi 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

Request for Question Clarification bywebsearcher-gaP.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 3×3 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

3×3 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 3×3 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 3×3 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 3×3 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

3×3 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 3×3 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

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.