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.

[img]http://www.ourspacer.com/misc/sudoku.jpg[/img]

My solver program shows it is solvable:

[spoiler]358617924
267489351
941325786
482753169
736891245
519264873
875936412
123548697
694172538[/spoiler]

I have no idea how it solved it though :(

[SPOILER]The cell in the lower-left corner is 6.[/SPOILER] 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.

[url]http://www.scanraid.com/sudoku.htm[/url]

YES.... this is the one I use when all else fails.
 

[url]http://www.scanraid.com/sudoku.htm[/url]

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 ....

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

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

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.

[quote=retina;129255]My solver program shows it is solvable:

I have no idea how it solved it though :([/quote]

Brute force (and ignorance)?

[quote=Fusion_power;129317]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[/quote]
See Markr's post for a very clear description of the "chain".

Only one other way? What is it?

[QUOTE=davieddy;129362]Brute force?[/QUOTE]I expect so. This computer is a brute, if I drop it on my toe it won't say sorry.