The New Sudoku Players' Forum

by **ghfick** » Tue May 03, 2016 6:10 pm

I am still primarily a pen and paper solver. I like to print off blank grids and print the givens on the grids. I also like to use the 'Extended Print' option in Bernhard Hobiger's 'HoDoKu' software. You can create and print off very demanding puzzles using this software. I use grids that are about the same size as those found in the newspapers. I print four grids to a page.
My solving proceeds in four steps:
1) I solve the puzzle as far as I can without any markings. This step typically takes me up to and including 'Locked Candidates' and 'Naked/Hidden Pairs/Triples'.
2) If the puzzle is not solved, I mark all cells using the standard 'key pad' system. I do not actually print the candidates' numbers but just print a dot in the appropriate position in the cell. This step usually takes me up to and including the 'Hard' strategies [as in HoDoKu's default Hard list]. As I identify exclusions, I place an X through the appropriate dot. If the puzzle gets too cluttered with X's, I use a simple liquid paper pen to take off the X's and dots. I then continue on with the consideration of XY-Chains [although considered 'Unfair' in HoDoKu] as I am fairly good at following the possible chains of bi-value cells. I will explore a possible chain only if there is a possibility of an exclusion.
3) If the puzzle is not solved after considering all the Hard strategies and XY-Chains, I then proceed to mark the strong links. I identify the strong links by column [vertical bar |], row [horizontal bar _ ] and box [diagonal line /] to surround a dot. [The three parts to a little right angled triangle] I do not find it necessary to further mark the bi-value cells. This marking method is a composite of Andrew Stuart's method and stk's method. I do not draw lines between the two cells and, for strong links in a box, I use a diagonal line while stk uses a dot [.] With the strong links marked, I am then able to consider AICs, Continuous Nice Loops and Discontinuous Nice Loops. Even with these markings, I identify ALS-XZ and ALS-XY in a very uncertain and haphazard way. Similarly, I occasionally find the simplest of Death Blossoms.
4) If the puzzle still is not solved, I have begun the explore the world of Exocet. David P Bird's compendium on JExocet is first rate. I am just a beginner here but this pattern does seem to be within the realm of human solving. David does refer to markings that may help to identify JExocet but I have not reached that stage yet. Also on my 'to do' list are posts by David P Bird on SK Loops and Braiding.

by **David P Bird** » Tue May 03, 2016 10:49 pm

ghfick, what you've described pleases me as it indicates I'm not entirely alone in sticking to my 'old school' principles here. This involves treating puzzles more like a game of patience than a race or a programming challenge. My aim is to push the envelope on the puzzles that can be solved without using branching of any sort other than that needed to prove the inferences from recognisable patterns.

However there is a lot of drudgery involved in solving using paper and pencil so I use a Sudoku Drudge spreadsheet to look after the mundane stuff. This allows me to fast-forward to the challenging parts of a puzzle. Like you I have devised a personal marking scheme, GEM, which I've described < here >.

If you're a stranger to SK loops let me warn you that there have been many heated discussions here about what is and what isn't a SK Loop and the logic behind them. My attempt to put the various issues to bed, < Domino Loops (SK Loops and Beyond) >, may help you.

I'd advise you to put Braiding right at to bottom of your 'to do' list. It's a lot of effort for little gain as in modest puzzles most of the inferences provided can be found far more simply. That said, the inferences in a JExocet band nearly all result from braiding considerations, and for those who like to solve without using pencil marks, an appreciation of braiding theory is useful.

DPB

by **SteveG48** » Wed May 04, 2016 1:00 pm

Hello, Ghfick. What you describe is also the way that I like to work the daily puzzles published in my local newspaper, though I prefer to work them in the paper rather than copying them out- sometimes a challenge with the small grids.

On the other hand, I also like to mix it up, using Hodoku to generate and work more difficult puzzles. A nice compromise that I also like to use from time to time is Pappocom's Sudoku program. It offers the convenience of an electronic game board without any of the automatic candidate tracking, filters, and other features that you find in the more advanced programs.

by **enxio27** » Wed May 04, 2016 9:33 pm

FWIW, I solve with pencil and paper, as well. Most of my sudoku time occurs before bed (helps my mind settle down for the night) or during my son's music lessons, or in short (5-10 minute) wait times here and there. I use standard, 9x9 "vanilla" puzzles to fill the short bursts of time, but for longer periods I like to do multi-grid puzzles of various types.

I have a collection of puzzles of varying difficulty. The 9x9 puzzles are sorted (on computer) and printed (using SadMan's Sudoku program) by difficulty (as rated by Sudocue). I haven't yet reached the 9x9 puzzles difficult enough to require pencil marks, but I know I will get to those before long. With the multi-grids, I use Richard Broughton's Sudoku Solver to print the grids with pencil marks. I initially tried writing my own pencil marks, but I found it far too tedious and mistake-prone before I ever got to the fun of solving the puzzle.

by **ghfick** » Thu May 05, 2016 11:43 pm

David: I am adding Graded Equivalence Marking to my 'to-do' list. Perhaps such marking might help with ALS-XZ, ALS-XY and related.
I am also interested in Sudoku Drudge. I do sometimes paste a puzzle into HoDoKu, let the solver take me to the first 'Hard' strategy and then print the puzzle and markings to that point. But I also still appreciate taking a puzzle from 'first principles'.
I will keep the pursuit of Braiding in neutral for the time being.
I gather that JExocet patterns will be in play only at early stages in a puzzle. If strong link marking turns up almost no strong links, maybe one can safely proceed to JExocet consideration without a detailed consideration of AICs et al. On the other hand, with almost no strong links, such an investigation will be short lived anyhow.

Steve: I do the 5 Star and 6 Star 'Universal Sudoku Puzzles' from our newspaper most nearly every week. I do try to solve them with no markings at all as a decent brain stretch. I will have a look at the Pappocom software.

enxio27: We do not get the multi grids in our newspaper but I do see them from time to time. Definite fun. I know of folk who like Killer Sudoku. I have played with them a bit but always return to the 'classic' Sudoku. Like you, I go to puzzles of varying difficulty. Currently, I generate puzzles using HoDoKu and all the defaults except that with XY-Chains set as 'Hard' and I expand Hard to the 3000 / 5000 HoDoKu range. This setting results in puzzles with paths needing lots of XY-Chains. Also yielding nice brain stretches.

Best
Gordon

by **SteveG48** » Thu May 05, 2016 11:58 pm

ghfick wrote:Steve: I do the 5 Star and 6 Star 'Universal Sudoku Puzzles' from our newspaper most nearly every week. I do try to solve them with no markings at all as a decent brain stretch. I will have a look at the Pappocom software.

enxio27: We do not get the multi grids in our newspaper but I do see them from time to time. Definite fun. I know of folk who like Killer Sudoku. I have played with them a bit but always return to the 'classic' Sudoku. Like you, I go to puzzles of varying difficulty. Currently, I generate puzzles using HoDoKu and all the defaults except that with XY-Chains set as 'Hard' and I expand Hard to the 3000 / 5000 HoDoKu range. This setting results in puzzles with paths needing lots of XY-Chains. Also yielding nice brain stretches.

I used to avoid PMs as well until forced into it, but more and more I find myself adding PMs even on easier puzzles. It often makes them go faster, and who wants to waste time on simple stuff?

by **Leren** » Fri May 06, 2016 12:41 am

Hi Gordon, if you want to practice finding Exocets, here is a list of puzzles that contain them. Be warned though, they are some of the most difficult puzzles, so you might have trouble solving them completely, but you will at least get practice finding the Exocets. The list tells you where they are, and their base digits.

Hidden Text: Show

Leren

by **David P Bird** » Fri May 06, 2016 7:01 pm

Gordon,

you wrote:I gather that JExocet patterns will be in play only at early stages in a puzzle.

That can be true but not always. JE inferences that were unavailable at the start may come into play later after other eliminations have been made when they can considerably shorten a solution.

David

by **enxio27** » Sun May 08, 2016 2:29 am

ghfick wrote:enxio27: We do not get the multi grids in our newspaper but I do see them from time to time. Definite fun. I know of folk who like Killer Sudoku. I have played with them a bit but always return to the 'classic' Sudoku. Like you, I go to puzzles of varying difficulty. Currently, I generate puzzles using HoDoKu and all the defaults except that with XY-Chains set as 'Hard' and I expand Hard to the 3000 / 5000 HoDoKu range. This setting results in puzzles with paths needing lots of XY-Chains. Also yielding nice brain stretches.

Other than Samurai (5-grid) puzzles, most of the multi-grid puzzles in my collection are from sites that no longer exist, such as Ruud's Sudocue.net and djApe's site. (I collected all of the specialty puzzles from Ruud's site and reposted them here: http://forum.enjoysudoku.com/ruud-s-specialty-puzzles-t31546.html If you enjoy the Clueless Specials, Clueless Explosions, and Samurai, I have those, as well, although not currently online.) There is another site I discovered fairly recently, vfalcone.ru, but you have to complete one puzzle before you can access the next. It has standard 9x9, Samurai, and Ninja (11-grid) puzzles. It will probably be a long time before I run out of puzzles and have to generate more using one of the programs I have.

I do a killer sudoku every now and then, but I prefer puzzles that use straight logic rather than those that also incorporating mathematics. I use sudoku primarily to relax and to tire my brain out before bed so that I can sleep. To me, killer sudoku is not relaxing.

It sounds as though your solving skills are considerably farther advanced than mine. I'm still trying to wrap my head around XY-chains.

by **ghfick** » Mon May 09, 2016 1:45 am

Steve: I do agree, in principle, about efficiency. I still have this grey zone when its comes to when I should markup. David refers to the Drudge. Marking up a puzzle is 'character building'. Sometimes I lose patience with a puzzle that appears to be elementary but the puzzle will not fall. Then, when I mark it up, I see that I missed a Naked Triple and I am a bit humbled. So, setting completely unnecessary constraints is part of the fun. Occasionally, for me, an aspect of a puzzle is seen that might be missed if a more structured [efficient?] approach had been applied.
Leren: Your JExocet list is soon going to occupy a considerable amount of my Sudoku time. Using David's Compendium, I now have a grasp of the pattern. Next, I will test myself with puzzles in your list. Then, I will enter the challenge of attacking puzzles that 'might' contain JExocet. Then, it is about adding the pattern to my lexicon. Maybe, at some future time, there will be the joy of identifying a JExocet without any 'help' at all. [well down the road for me]
David: Your compendium currently dominates my Sudoku time. It will be interesting to see puzzles with a late(r) arrival of a JExocet.
enxio27: Thanks for the link. Please do repost the others to keep them in action. Up until quite recently, I saw XY-Chains as too daunting. I first saw the alternate logic to place the XY-Wing as the simplest [shortest] XY-Chain. Then, I used the preferences in Hodoku to create puzzles with short XY-Chains [go to Steps and change the chain length from the default]. I practiced these short ones for a while. Then, I read:
https://sysudoku.com/2011/12/06/xy-web/
I have not been able to incorporate 'XY Railroads' into my approach, but this post did enable me to see the chain's length as just a descriptor and not a obstacle.

Best
Gordon

by **enxio27** » Mon May 09, 2016 2:32 pm

ghfick wrote:enzio27: Thanks for the link. Please do repost the others to keep them in action.

Now that I think of it, all of Ruud's Clueless Specials, Clueless Explosions, and Samurai have been reposted to Richard Broughton's Sudoku Solver forum by one of the admins there, along with many others that have been created since then by forum members. There is a forum section devoted to each of those three puzzle types, as well as one for killers, one for other gattai (multi-grid puzzles) and another for other variants (jigsaw, windoku, anti-chess, etc.).

Up until quite recently, I saw XY-Chains as too daunting. I first saw the alternate logic to place the XY-Wing as the simplest [shortest] XY-Chain.[/quote]
I still haven't gotten the hang of XY-Wings yet. I guess that's next on the list. Thanks for the suggestion and the link!

by **ghfick** » Thu May 19, 2016 10:47 pm

I have attached two files. One shows the strong links with the components of a little triangle using a file developed by John Welch. [sysudoku.com] The other is an actual handwritten puzzle near completion [using the little triangles]

by **ghfick** » Sun Dec 17, 2017 12:51 am

It has been a while since I contributed to this thread. My method has not changed materially in the past year or so. I still miss Naked Triples and Hidden Triples, Quads, Quints... rather often.
I would say I am comfortable and structured with the 'Hard' strategies based on the grid markup. I usually start with the Two String Kite, then I move on to the XY-Wing and the XYZ-Wing. Then onto the UR and then those moves that need a look at the strong links including the W Wing, Empty Rectangles and the Finned X Wing.
When I feel I must do the strong link markup, I sense that the puzzle is in the 'Unfair' range. I am still not very good with AICs generally and I remain quite hopeless with ALS based moves.
I have now spent considerable time with David P Bird's JE compendium. Highly recommended to all. Further, one can make advances with very demanding puzzles when the initial JE appears. Sometimes, the JE and the derived inferences crack a really tough puzzle.
Parts of the SK Loop, MSLS and MultiFish world are definitely available to human solvers. For me, the catch is that while one might get a flurry of exclusions from these moves with extreme puzzles, the puzzles typically remain unsolvable [with only non-assumptive moves].
I am interested in some recent developments that uncover patterns with ALS moves that appear to be available to human solvers. StrmCkr has contributed and organized a wealth of these options.

by **StrmCkr** » Sun Dec 17, 2017 5:13 am

Thanks, happy to help.

by **SpAce** » Sun Dec 17, 2017 11:27 pm

Hi ghfick. Nice to get a glance at someone else's manual solving system. I'm a pure pencil-and-paper solver and have created my very own system like you. Its basic version has similar features to yours (plus/minus some), though the implementation and focus are quite different (I mostly look for generic AICs/loops instead of named patterns). I'll probably post it here one of these days, and it would be interesting to hear your comments. It's going to take quite a few photographs, though, and I was wondering what the forum rules are about posting those (size etc)?

I've also created a hardcore version which kicks butt on more difficult puzzles, but it requires a bigger than normal grid and is so feature-rich (=complicated) that I doubt anyone besides myself would have the patience to use it manually. It'd probably work best as a software implementation, but I don't know if I'll ever get around to coding it. I'm personally quite comfortable using it with just pencil-and-paper, though.

The New Sudoku Players' Forum

I am primarily a pen and paper solver

I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver

Re: I am primarily a pen and paper solver