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 Subject: Sudoku Category: Miscellaneous Asked by: tvilfr-ga List Price: \$20.00 Posted: 19 Jul 2005 14:32 PDT Expires: 18 Aug 2005 14:32 PDT Question ID: 545488
 ```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 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``` 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.``` 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``` Request for Question Clarification by websearcher-ga on 23 Jul 2005 20:55 PDT `P.S. I'll also find those resources you want.`
 Subject: Re: Sudoku Answered By: websearcher-ga on 24 Jul 2005 08:43 PDT Rated:
 ```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``` 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.```
 tvilfr-ga rated this answer: ```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.```

 Subject: Re: Sudoku From: nproctor-ga on 19 Jul 2005 15:57 PDT
 ```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!```
 Subject: Re: Sudoku From: pugwashjw-ga on 19 Jul 2005 20:21 PDT
 ```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.```
 Subject: Re: Sudoku From: cheyuta1939-ga on 23 Jul 2005 09:30 PDT
 ```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```
 Subject: Re: Sudoku From: lisarea-ga on 23 Jul 2005 09:47 PDT
 ```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.```
 Subject: Re: Sudoku From: nproctor-ga on 01 Aug 2005 02:54 PDT
 ```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.```