Sudoku puzzle help

JuanTutors · 2008-03-20, 04:52

I'm having a hell of a time with this sudoku puzzle. I've never gotten to a point that a puzzle would take me even close to an hour, except for this puzzle.

What I would like from you puzzle geniuses:

1. I'm pretty sure there are no mistakes. I checked it over. But If I made an error, tell me what it is.

2. Otherwise, find a number and tell me how you found it.

The black numbers are the numbers the puzzle came with. The grey numbers are the numbers I entered.

http://www.ourspacer.com/misc/sudoku.jpg

retina · 2008-03-20, 05:14

My solver program shows it is solvable:

358617924
267489351
941325786
482753169
736891245
519264873
875936412
123548697
694172538

I have no idea how it solved it though :(

markr · 2008-03-20, 05:56

The cell in the lower-left corner is 6. From there it falls out.

I got to where you did no problem, then was lucky with a method I'm just starting to get the hang of. If you look at the five cells highlighted blue, they all have just two possible numbers, and form a chain (3,7) (7,1) (1,3) (3,1) (1,3). If the first cell is not 3, it's 7, so the next cell in the chain is 1, and so on until the last one is 3. Either way, at least one end of the chain is a 3. So the lower-left-corner cell can't be 3, leaving just one possibility.

There's probably other ways to get to the solution.

Kees · 2008-03-20, 11:32

http://www.scanraid.com/sudoku.htm

petrw1 · 2008-03-20, 19:20

http://www.scanraid.com/sudoku.htm

It is by far the smartest "I have found" so far .... meaning I haven't checked out every one (by no means) but when I found this one I was impressed.

It has many VERY advanced techniques and as a bonus it has links to describe these techniques ... AND ... if all else fails it has links to another very advanced site complete with a forum.

Go crazy ....

Fusion_power · 2008-03-21, 01:10

When I first saw this one I hoped it would be really hard. It took about 20 minutes.

It is VERY susceptible to chain analysis.

DarJones

Fusion_power · 2008-03-21, 01:43

Just so an explanation is given for the problem posed, here is the way it should be analyzed.

Look at cell A5. This is the cell at top center. Only two possibilities can fit, either 1 or 7. Regardless of what value you put in this cell, the only value that can possibly fit in cell I1 is 6. This is the cell at the bottom left corner. You can find this referred to as a "forced chain".

There is one other way to analyze this but the above is the simplest.

DarJones

JuanTutors · 2008-03-21, 04:22

I'll look up this article on sudoku. I like coming up w/ the tricks myself, but I never learned this "forced chain" concept. I've used it before, but it never seemed so viable. Maybe there's a smart way of knowing where to start looking? I don't use notes.

davieddy · 2008-03-21, 15:17

Quote:

Originally Posted by retina

My solver program shows it is solvable:

I have no idea how it solved it though :(

Brute force (and ignorance)?

davieddy · 2008-03-21, 15:20

Quote:

Originally Posted by Fusion_power

Just so an explanation is given for the problem posed, here is the way it should be analyzed.

There is one other way to analyze this but the above is the simplest.

DarJones

See Markr's post for a very clear description of the "chain".

Only one other way? What is it?

retina · 2008-03-21, 15:31

Quote:

Originally Posted by davieddy

Brute force?

I expect so. This computer is a brute, if I drop it on my toe it won't say sorry.

2008-03-20, 04:52	#1
JuanTutors "Juan Tutors" Mar 2004 571 Posts	Sudoku puzzle help I'm having a hell of a time with this sudoku puzzle. I've never gotten to a point that a puzzle would take me even close to an hour, except for this puzzle. What I would like from you puzzle geniuses: 1. I'm pretty sure there are no mistakes. I checked it over. But If I made an error, tell me what it is. 2. Otherwise, find a number and tell me how you found it. The black numbers are the numbers the puzzle came with. The grey numbers are the numbers I entered. http://www.ourspacer.com/misc/sudoku.jpg

2008-03-20, 05:56	#3
markr "Mark" Feb 2003 Sydney 3×191 Posts	The cell in the lower-left corner is 6. From there it falls out. I got to where you did no problem, then was lucky with a method I'm just starting to get the hang of. If you look at the five cells highlighted blue, they all have just two possible numbers, and form a chain (3,7) (7,1) (1,3) (3,1) (1,3). If the first cell is not 3, it's 7, so the next cell in the chain is 1, and so on until the last one is 3. Either way, at least one end of the chain is a 3. So the lower-left-corner cell can't be 3, leaving just one possibility. There's probably other ways to get to the solution. Attached Thumbnails

2008-03-20, 19:20	#5
petrw1 1976 Toyota Corona years forever! "Wayne" Nov 2006 Saskatchewan, Canada 5²×211 Posts	YES.... this is the one I use when all else fails. http://www.scanraid.com/sudoku.htm It is by far the smartest "I have found" so far .... meaning I haven't checked out every one (by no means) but when I found this one I was impressed. It has many VERY advanced techniques and as a bonus it has links to describe these techniques ... AND ... if all else fails it has links to another very advanced site complete with a forum. Go crazy ....

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
a partial sudoku puzzle	MattcAnderson	Miscellaneous Math	4	2017-06-29 07:14
An auto-eroica sudoku	Batalov	Puzzles	21	2015-06-24 10:24
Sodyoutoo (a.k.a. Sudoku)	mwxdbcr	Puzzles	15	2015-05-17 05:27
a puzzle	bcp19	Puzzles	18	2012-03-02 04:11
Dot puzzle	nibble4bits	Puzzles	37	2006-02-27 09:35

2008-03-20, 05:14	#2
retina Undefined "The unspeakable one" Jun 2006 My evil lair 5·7·191 Posts	My solver program shows it is solvable: 358617924 267489351 941325786 482753169 736891245 519264873 875936412 123548697 694172538 I have no idea how it solved it though :(

2008-03-20, 11:32	#4
Kees Dec 2005 11000100₂ Posts	http://www.scanraid.com/sudoku.htm

2008-03-21, 01:10	#6
Fusion_power Aug 2003 Snicker, AL 3C0₁₆ Posts	When I first saw this one I hoped it would be really hard. It took about 20 minutes. It is VERY susceptible to chain analysis. DarJones

2008-03-21, 01:43	#7
Fusion_power Aug 2003 Snicker, AL 2⁶×3×5 Posts	Just so an explanation is given for the problem posed, here is the way it should be analyzed. Look at cell A5. This is the cell at top center. Only two possibilities can fit, either 1 or 7. Regardless of what value you put in this cell, the only value that can possibly fit in cell I1 is 6. This is the cell at the bottom left corner. You can find this referred to as a "forced chain". There is one other way to analyze this but the above is the simplest. DarJones

2008-03-21, 04:22	#8
JuanTutors "Juan Tutors" Mar 2004 1073₈ Posts	I'll look up this article on sudoku. I like coming up w/ the tricks myself, but I never learned this "forced chain" concept. I've used it before, but it never seemed so viable. Maybe there's a smart way of knowing where to start looking? I don't use notes.