## Need solving technique explained

Advanced methods and approaches for solving Sudoku puzzles

### Need solving technique explained

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

Posts: 13
Joined: 13 October 2005

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
CathyW

Posts: 316
Joined: 20 June 2005

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

Posts: 13
Joined: 13 October 2005

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.
Shazbot

Posts: 220
Joined: 24 September 2005

### Re: Need solving technique explained

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
Cec

Posts: 1039
Joined: 16 June 2005

[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

Posts: 13
Joined: 13 October 2005

### Re: To cecbevwr

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

Posts: 13
Joined: 13 October 2005

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.
Shazbot

Posts: 220
Joined: 24 September 2005

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

Posts: 13
Joined: 13 October 2005

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!
Shazbot

Posts: 220
Joined: 24 September 2005

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.
PaulIQ164

Posts: 533
Joined: 16 July 2005