## Very Hard puzzle - can't find next step

Advanced methods and approaches for solving Sudoku puzzles

### Very Hard puzzle - can't find next step

*8* **2 ***
1*4 57* 2*3
7** *** ***

8*3 1*7 492
*47 *2* 158
2*1 8*4 637

4** 7** **9
5*6 48* **1
*** 2** *4*

Can somebody give me a hand?

Last edited by doku on Sat Sep 10, 2005 6:40 am, edited 1 time in total.
doku

Posts: 5
Joined: 10 September 2005

Concentrate on candidate 5's. There are a number of eliminations that can be made, followed by a placement in row 2.
SteveF

Posts: 86
Joined: 26 March 2005

I know, i found that 5 already but i didn't place it in my first post. Do you have another hint?
doku

Posts: 5
Joined: 10 September 2005

Look for a triple in column 2, this should allow a candidate to be placed in row 8.
SteveF

Posts: 86
Joined: 26 March 2005

Thanks, but what is meant by a "triple" ?
doku

Posts: 5
Joined: 10 September 2005

doku wrote:Thanks, but what is meant by a "triple" ?

doku -

Check the candidates in column 2 for rows 2, 4 & 6...

3 numbers, spread across 3 cells - therefore those numbers cannot be candidates in rows 7, 8 & 9 (still looking at column 2 here).

This forces a number into the bottom row of the bottom left block, which enables you to place that number in the bottom middle block.
whohe

Posts: 32
Joined: 28 May 2005

It is probably worth going to one of the excelent sites for descriptions of some of the techniques such as triples.

http://www.simes.clara.co.uk/programs/sudokutechniques.htm

http://www.angusj.com/sudoku/

These are both well worth a visit.
SteveF

Posts: 86
Joined: 26 March 2005

whohe wrote:Check the candidates in column 2 for rows 2, 4 & 6...

3 numbers, spread across 3 cells - therefore those numbers cannot be candidates in rows 7, 8 & 9 (still looking at column 2 here).

This forces a number into the bottom row of the bottom left block, which enables you to place that number in the bottom middle block.

I still don't see it, can you explain it further?
doku

Posts: 5
Joined: 10 September 2005

In column 2:

r2c2 can be 6 or 9

r4c2 can be 5 or 6

r6c2 can be 5 or 9

Thus the only three valid candidates for these 3 cells are 5, 6 and 9. Thus the candidates 5, 6 and 9 must go in these three cells and nowhere else. Thesrefore you can eliminate these as candidates from all other cells in column 2.

Having done these eliminations, what is the only value that can go in r8c6?
SteveF

Posts: 86
Joined: 26 March 2005

Hi,

Here is the answer, I use a Excel to support to solve.

685932714
194578263
732641985
863157492
947326158
251894637
418763529
526489371
379215846[/img]
SkyWu

Posts: 1
Joined: 10 September 2005

I'm going to post all mine here in future, then you can just tell me the answers so I won't have to do them anymore. Imagine the time it'll free up in my working day.

Oh yeah, forgot, don't have a job.
Karyobin

Posts: 396
Joined: 18 June 2005

SteveF wrote:In column 2:

r2c2 can be 6 or 9

r4c2 can be 5 or 6

r6c2 can be 5 or 9

Thus the only three valid candidates for these 3 cells are 5, 6 and 9. Thus the candidates 5, 6 and 9 must go in these three cells and nowhere else. Thesrefore you can eliminate these as candidates from all other cells in column 2.

Having done these eliminations, what is the only value that can go in r8c6?

Thanks for the explanation. Somehow i was distracted by the possibility that the 6 or 9 also could go anywhere else in this column. But it isn't. I prefer this method to find the answer rather than the whole solution. Because with the SteveF method i can learn the techniques step by step.

By the way, that hint was the one that solved me the puzzle!
doku

Posts: 5
Joined: 10 September 2005

I like the 'SteveF method' too, even if it does sound like a form of birth control.
emm

Posts: 987
Joined: 02 July 2005