Intelligible human-solving techniques beyond Simple Sudoku?

Advanced methods and approaches for solving Sudoku puzzles

Intelligible human-solving techniques beyond Simple Sudoku?

Postby xetnauq » Tue Sep 11, 2007 3:40 am

Playing with Simple Sudoku (nice program), I've gotten to the point that the Expert puzzles are far too easy and the Extreme puzzles, while solvable, are annoying. I don't like the XY-Wing technique much, since it requires laboriously checking tons of cells, and the Extreme puzzles use it all the time.

I'm looking for recommendations on some other techniques out there that are:

a. easily understandable and human-solvable (using a program like Simple Sudoku)

b. unique and not completely covered already by the ones used by Simple Sudoku (simple coloring, multicoloring, X-Wing, Swordfish...)

c. commonly useful (show up a lot)

d. fun (not a requirement, but up till XY-Wing, I thought most of the previous techniques, e.g. coloring, were kind of fun)

I looked at Remote Pairs, which I don't get because it seems completely covered by Simple Coloring, which isn't a difficult concept. I learned X-Colors as well, which I find a bit useful although it doesn't seem to cover all the positions that Multicolors does, as Sudopedia claims. I'm a little confused that many of the techniques seem to be essentially the same concepts with different names - and I don't see many sites that have tried to resolve the differences and pick out the most useful ones.

Does anybody have any recommendations on relatively simple, useful, unique techniques to learn?
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Postby re'born » Tue Sep 11, 2007 10:37 am

Try downloading Ruud's software SudoCue. It's got a large collection of techniques of which the Simple Sudoku techniques are a subset and the online help is very useful.
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Postby Bigtone53 » Tue Sep 11, 2007 1:35 pm

I don't like the XY-Wing technique much, since it requires laboriously checking tons of cells, and the Extreme puzzles use it all the time.

I play with Simple Sudoku to keep my brain alive and enjoy finding the XY-wings when they appear (which is as you say quite often but not always). The Ctrl-Y key almost highlights them.

I have never been able to get my brains around colouring and multiple colouring, although you treat these as easier techniques. It is all in the eyes perhaps:D
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Postby Mike Barker » Wed Sep 12, 2007 2:30 am

If you enjoy colouring, John MacLeod has developed a simple extension which will help find things like xy-wings. Its on the Eureka forum so beware, reading may not be fun (or maybe it will be depending on your sense of humor). I believe that there was some issue as well, which maybe Ron can help clarify. Anyway, consider yourself warned, but you might check out xy-colouring
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Postby sirdave » Wed Sep 12, 2007 4:20 pm


When one is trying to advance in Sudoku the variations in names and what appears to be a morass of various solving techniques can make it difficult to make sense of it all. One place to start is Andrew Stuart's 'The Logic of Sudoku' book or some of the tutorials by Ruud (Sudocue), Paul Stephens etc.

The fact that you are having a bit of an issue with XY-wings is more an indication of the puzzle level you are at than their actual importance in overall solving. In other words, as you advance to the more difficult puzzles, XY-wings actually play only a minor role in the overall solving. In fact, sometimes you may find that in a very difficult puzzle, the mere finding of an XY-wing will seem like manna from Heaven!:)

FWIW: I would stay away from x-colouring, however, Mike's suggestion to check out xy-colouring at Eureka is a good one, but as Mike infers don't be dismayed by some of the 'crazy-making' you may run into in the discussions associated with it.
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Postby xetnauq » Mon Sep 17, 2007 2:13 am

Thanks for the replies - these were all very helpful and pointed me in the right direction.

I played a bit with xy-coloring, at least as I understood it, using Sudocue's ultracolors. Looks neat - of course you're not going to be able to do that with Simple Sudoku, but that's fine. Oddly, immediately I started running into instances where logically I was positive I'd need to color both candidates of a single "bivalue cell" red (a case he didn't seem to cover - and one that would result in a whole chain of dual reds)... so I just stopped at that point and switched over to blue. Maybe I made a mistake somewhere else - but I couldn't find one. It seemed to work to solve a few simple XY-wings - and admittedly was a lot more fun (but took longer) than the XY-wings. I figure if it'll also solve harder problems as claimed it'll be extremely helpful.

I'd downloaded Sudocue a long time ago but wasn't sure where to get started with it... but I just installed it again. Looks like it offers many solving possibilities compared to Simple Sudoku, but requires some tuning and adjustment to new techniques. I think it'll offer up a lot of opportunities to learn something new.
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This is exactly what I am talking about

Postby drstephenkerr » Thu Oct 11, 2007 12:16 am

I had the same feelings about sudoku, make it more fun and less laborious. I read all of the books, looked at all of the 'collection of solving techniques' etc.
The book I wrote called Top Secret Sudoku System is exactly that, a Human Solvable system, not a collection of techniques. Minimizes penciling in, and makes solving puzzles more fun. the system is also not complete, there are some situations that I encounter that I just know there is a 'logical' explanation for, mainly in the Expert puzzles from published books like Michael Rios' Mensa Sudoku and Wayne Gould's Super Sudoku etc. That said, there are maybe 5 or 6 puzzles in any of that level of book that give the system a run for its money.
I will give you some hints as to the system and how it works via e-mail, I don't want to post them because...well...the book is for sale, but I would like to see what you think of the system from the perspective of the question referred to in your post.
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Postby Sped » Thu Oct 18, 2007 4:58 pm

I use Simple Sudoku a lot, and I've developed an easy and fun (for me, anyway) technique to find xy chains, including 3 cell xy chains, aka xy Wings.

I explained the techinque here:

I find xy chains all the time on extreme puzzles. It's kind of disappointing when the chain turns out to be only 3 cells long, i.e. an xy wing.
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Postby re'born » Thu Oct 18, 2007 8:38 pm

xetnauq wrote:I looked at Remote Pairs, which I don't get because it seems completely covered by Simple Coloring, which isn't a difficult concept.

Excellent! Historically, I think remote naked pairs was noticed first which is why it ended up with a name despite it being just two simultaneous applications of simple coloring. Anyway, since you understand it, why not try the slightly more general semi-remote naked pair? Speaking of which,

This is a fine example Sped links to and I think his exposition there is top notch. I just took a peek at the puzzle itself and:
Code: Select all
 | 3689  39    368   | 89    5     2     | 7     1     4     |
 | 79&   2     4     | 79*   3     1     | 5     8     6     |
 | 78    5     1     | 4     6     78*   | 3     9     2     |
 | 368   37    368   | 1     2     578*  | 4     57    9     |
 | 59-   79&   58    | 6     78*   4     | 1     2     3     |
 | 1     4     2     | 3     9     57*   | 8     6     57    |
 | 45    1     9     | 78    478   6     | 2     3     57    |
 | 2     6     7     | 5     1     3     | 9     4     8     |
 | 345   8     35    | 2     47    9     | 6     57    1     |

There is an obnoxious semi-remote naked pair (using grouped links) that eliminates 9 from r5c1. The point is that I found this quite quickly using Simple Sudoku. First I highlighted pairs to find two bivalued cells with same candidates. Upon seeing the the <79> in r2c1 and r5c2, I also noticed the potential elimination of 9 in r5c1. So I switched the filter to 7's and traced alternating weak and strong links. I didn't even need to use colors (though certainly one could). And most semi-remote naked pairs are much easier to spot than this one.
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Easier systems

Postby sudokumaestro » Thu Jul 10, 2008 5:25 am

I am not sure about this forum, it has been a long time without a post.
But you should check out the dottin system by Alex D La Barba, in Seattle, it is an interesting and simple marking technique. Refreshing.
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Re: Easier systems

Postby Luke » Sat Jul 12, 2008 9:58 pm

sudokumaestro wrote:.... you should check out the dottin system by Alex D La Barba, in Seattle, it is an interesting and simple marking technique. Refreshing.

Thanks, I did. Now I know that a certain Mr. La Barba of Seattle invented PM's on June 12, 2008 (last month.) Later the same day, he revealed the concept of naked pairs, which he had "personally developed."

Quite a burst of innovation by any standard.....
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comgeek puters

Postby sudokumaestro » Sun Jul 13, 2008 3:31 am

"try dottin"
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