Need solving technique explained

Advanced methods and approaches for solving Sudoku puzzles

Need solving technique explained

Postby gklittle » Sun Oct 23, 2005 1:43 pm

Hello,
I'm still trying to master (LOL) sudoku! I get stumped on the very hard ones (and some hard ones).

I have reached a stopping point in this puzzle. Unless I have missed a simple step, I think I need some techniques that I haven't mastered (there are many!!)

I copied the puzzle to simple sudoku, clicked the question mark and column 7 was highlighted in blue and yellow. I then clicked solve next step and the blue remained unchanged, the yellow squares were reduced.
The column is as follows:

57
357 (reduced to 3)
4
6
289 (reduced to 89)
27
25
3589(reduced to 389)

I would appreciate someone explaining the reductions in this column to me. Thanks so much.

P.S. Any other hints would be appreciated!!!!!



*-----------*
|94.|..3|.26|
|.6.|9.4|.18|
|1..|26.|49.|
|---+---+---|
|894|327|651|
|...|..6|...|
|.16|.89|.3.|
|---+---+---|
|731|.9.|.6.|
|48.|6.2|17.|
|62.|7.1|...|
*-----------*




*-----------------------------------------------------------*
| 9 4 78 | 158 157 3 | 57 2 6 |
| 235 6 237 | 9 57 4 | 357 1 8 |
| 1 57 378 | 2 6 58 | 4 9 357 |
|-------------------+-------------------+-------------------|
| 8 9 4 | 3 2 7 | 6 5 1 |
| 235 57 237 | 15 145 6 | 289 48 29 |
| 25 1 6 | 45 8 9 | 27 3 247 |
|-------------------+-------------------+-------------------|
| 7 3 1 | 458 9 58 | 25 6 245 |
| 4 8 59 | 6 35 2 | 1 7 359 |
| 6 2 59 | 7 345 1 | 3589 48 359 |
*-----------------------------------------------------------*
gklittle
 
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Postby CathyW » Sun Oct 23, 2005 2:03 pm

You have a pair (89) in r5,c7 and r9,c7 which means you can eliminate the 3 and 5 from r9,c7 and the 2 from r5,c7. Therefore r2,c7 is the only cell left in that column where the 3 can go.

HTH
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Postby gklittle » Sun Oct 23, 2005 2:58 pm

I can't believe I missed the pair!!!!!!
Thanks.
I'll check back in on my next stumbling block
gklittle
 
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Joined: 13 October 2005

Postby Shazbot » Mon Oct 24, 2005 5:15 am

you also have a naked triple of [2 5 7] in rows 1, 7 and 8, which means you can eliminate those numbers from all other cells in that column. Would give you the same results.

Edit: sorry - rows 1, 6 and 7. You've left out the 1 from row 8 in your original candidate list
Last edited by Shazbot on Mon Oct 24, 2005 5:19 pm, edited 1 time in total.
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Re: Need solving technique explained

Postby Cec » Mon Oct 24, 2005 6:35 am

gklittle wrote:I'm still trying to master (LOL) sudoku! ... Unless I have missed a simple step, I think I need some techniques that I haven't mastered (there are many!!)


Hi gklittle, I don't know what (LOL) sudoku is but the following sites provide excellent solving techniques if you haven't looked at these yet.

(a) http://www.simes.clara.co.uk/programs/sudokutechniques.htm
(b) http://www.angusj.com/sudoku/hints.php

Bonsai Cec
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Postby gklittle » Mon Oct 24, 2005 1:28 pm

[quote="shazbot"]you also have a naked triple of [2 5 7] in rows 1, 7 and 8, which means you can eliminate those numbers from all other cells in that column. Would give you the same results.[/quote]

I'm not seeing the naked triple. Which column, please?
gklittle
 
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Joined: 13 October 2005

Re: To cecbevwr

Postby gklittle » Mon Oct 24, 2005 1:35 pm

Hi gklittle, I don't know what (LOL) sudoku is but the following sites provide excellent solving techniques if you haven't looked at these yet.

(a) http://www.simes.clara.co.uk/programs/sudokutechniques.htm
(b) http://www.angusj.com/sudoku/hints.php



Thanks for the sites. I'm still working on understanding some of the techniques. LOL means "laughing out loud" at the thought of me mastering Sudoku!
gklittle
 
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Joined: 13 October 2005

Postby Shazbot » Mon Oct 24, 2005 9:14 pm

gklittle wrote:I'm not seeing the naked triple. Which column, please?

in your list of candidates for column 7:

57
357 (reduced to 3)
4
6
289 (reduced to 89)
27
25
1 (which you left out of your original list)
3589(reduced to 389)

2, 5 and 7 can be eliminated from all other cells, leaving you with 3 in row 2, 89 in row 5 and 389 in row 9.
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Postby gklittle » Mon Oct 24, 2005 11:56 pm

Thanks Shazbot,

My understanding of the naked triple is fuzzy. I thought a 25, 27, 275 was one, I didn't realize it could be 25, 27, 57 with a 5 in another box. I will have to work on that!
[/quote]
gklittle
 
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Postby Shazbot » Tue Oct 25, 2005 5:25 am

yeah, because the only candidates for those three boxes COMBINED is 2, 5 and 7, so those numbers MUST be in those boxes in some order. You can then remove them from all others.

It's the HIDDEN triples that I'm wrestling with now!
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Postby PaulIQ164 » Tue Oct 25, 2005 9:40 am

Hidden triples are much easier to find in normal pulles than in lists of candidates. Look at this:

Code: Select all
   ¦3  ¦16
52 ¦164¦   
   ¦98 ¦   
---+---+---
   ¦   ¦  5
   ¦   ¦  2
...etc


With a hidden single, you're thinking "where on this row can the 3 go?", and you find there's only one place. With hidden pairs, you're thinking say, "Where in this row can the 2-and-5 go?", and you hope to find there's only one place (a 'place' in this case obviously being two cells). So in this example, look where the 2 and 5 can and can't go on row 1. They clearly can't go in cells 1,2,3 because of the 2 and 5 in box 1. The 2 and 5 in column 9 stops them being there. This means the 2 and 5 must go in r1c5 and r1c6 in some order. In this example that means you know what goes in the last empty space of box 2.
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