Where to find extreme(+) puzzles?

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Where to find extreme(+) puzzles?

Postby SpAce » Fri Sep 01, 2017 10:35 pm

Can anyone point to good sources of extreme(+) puzzles? My current level is such that I can pretty comfortably complete SudoCue Sunday Nightmares. They're surely challenging enough for enjoyment, but I'd also like to take stabs at (slightly) higher levels to find my limits and to learn some new tricks. In terms of SudokuWiki grading, the nightmares have been between 600-900 points, and so far I've had no big problems with them. I've yet to make even a mistake, even though I work with pencil-and-paper only. However, I failed at a 1500-point puzzle I recently tried (and I know why), so I guess that's around the level I'm looking for next. I just don't know where to find more of them.

I only started studying and applying advanced techniques earlier this year, so this is all pretty new to me. Before then I could only solve basic puzzles and some tough ones (by guessing, yuck). Thanks to all the helpful information here and elsewhere, solving is now much more fun than I could have imagined! A lot more to learn, I'm sure.
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Re: Where to find extreme(+) puzzles?

Postby eleven » Sun Sep 03, 2017 9:26 pm

SpAce wrote:Can anyone point to good sources of extreme(+) puzzles? My current level is such that I can pretty comfortably complete SudoCue Sunday Nightmares.

So i guess, that also the tough puzzles at http://sudoku.com.au/ are not hard enough for you.
I don't know a site, which regularly publishs harder puzzle. Simply, because there is too little interest in that.

In the Pattern Games Results thread you can find lists of puzzles (each in one line) with the Sudoku Explainer rating at the end of the line. Probably the nightmares would have 7.3 to 7.8, but i did not check.
So you can start with say 8.0, which probapbly is harder, but in most cases solvable with the same techniques.

People who solve 9+ puzzles more than one time are very rare. Not because others could not, but in fact this is very time consuming and boring - if you don't know, that for that particular puzzle a special technique (like exocet) can help you.
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Re: Where to find extreme(+) puzzles?

Postby Leren » Sun Sep 03, 2017 11:05 pm

You might try the Exotic Patterns thread here.

Also, to get you started, here are some difficult puzzles that are famous enough to have been given names.

Hidden Text: Show
Code: Select all
Bronze Medalian #      1.......7.2.4...6...3...5...9..82.......9..8....6..4....5...1...6.8...2.7....3...               
Cheese      .2..5.7..4..1....68....3...2....8..3.4..2.5.....6...1...2.9.....9......57.4...9..                
Cigarette      12.3.....34....1....5......6.24..5......6..7......8..6..42..3......7...9.....9.8.               
Cloudy Bay #      1.........2.4...6...3...5.1.4..86.......49.8....2.....5.7...3...6.9...4.........7               
Deskarati      ..53.....8......2..7..1.5..4....53...1..7...6..32...8..6.5....9..4....3......97..               
Discrepancy      12.4..3..3...1..5...6...1..7...9.....4.6.3.....3..2...5...8.7....7.....5.......98               
DukDiamond1 #      1.......2.2.....6...34..5.....8.5.....8.3.9.....9.4.....5..34...7.....1.6.......7               
DukDiamond2 #      1.......2.2.....6...34..5.....8.5.....8.3.9.....9.4.....53..4...6......77......1.               
Easter Monster      1.......2.9.4...5...6...7...5.9.3.......7.......85..4.7.....6...3...9.8...2.....1               
Escargot      1....7.9..3..2...8..96..5....53..9...1..8...26....4...3......1..4......7..7...3..               
Fata Morgana      ........3..1..56...9..4..7......9.5.7.......8.5.4.2....8..2..9...35..1..6........               
First_Peak      12.3.....4...5......6..17..5..2......3..1..4...1..68....9....7....1..9.......9.68               
Golden Nugget #      .......39.....1..5..3.5.8....8.9...6.7...2...1..4.......9.8..5..2....6..4..7.....               
Green Glasses (FM)      .2.4.....4....92...98.....4...6....75...1.....4...38..3......6....7....1..4..85..               
Imam_bayildi      ..3..6.8....1..2......7...4..9..8.6..3..4...1.7.2.....3....5.....5...6..98.....5.               
Kolk      12.3.....4.....3....3.5......42..5......8...9.6...5.7...15..2......9..6......7..8               
Patience      12.3.....4.5...6...7.....2.6..1..3....453.........8..9...45.1.........8......2..7               
Platinum Blonde #      .1.2....3..4.5....6....7.....7.4....5....6....2.8...9..3..........9...31......729               
Pretty Biest      5..6......2.....4...1.2.3..9..8.......7.4.1.......9..6..4.7.2...3.....1......5..8               
Red Dwarf      12.3....435....1....4........54..2..6...7.........8.9...31..5.......9.7.....6...8               
Silver Plate #      1.......7.2.4...6...3...5...9..4........62.4....9..8....5.....3.6.2...8.7....1...               
Tarx0001      ........3..1..56...9..4..7......9.5.7.......8.5.4.2....8..2..9...35..1..6........               
Trompel'oeil       ........2..1...7...3..5..9......6.4...3.4.8...4.5.9....9..6..3...2...1..7....3...               
Tungston Rod #      ........7.2.4...6.1.....5...9...2.4....8..6..6..9.......5..3....3..8..2.7....4..1               
WeeKender1 #      ........91......35..9.3.8....3.5...67....2......4.......6.8..9..2.7..6..4.....1..               
WeeKender2 #      ..1.....7.2..4..6.3.....5...9.4.6.......92.4.......8....7..3....6..2..8.5.......1

Another good resource is the JExocet Compendium here.

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Re: Where to find extreme(+) puzzles?

Postby Cenoman » Mon Sep 04, 2017 8:51 pm

In addition to Leren's post, may be could you find weekly opportunities to put advanced techniques in practise here

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Re: Where to find extreme(+) puzzles?

Postby eleven » Mon Sep 04, 2017 9:25 pm

To speak it out.
Lerens puzzles are some of the hardest known, and you might notice, that the commentators of the extreme puzzle in Cenoman's link are programmers.
Those are puzzles rated 10+ by the Sudoku Explainer.
You should not be too ambitious, when looking for harder ones.
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Re: Where to find extreme(+) puzzles?

Postby Leren » Mon Sep 04, 2017 9:41 pm

Perhaps your best option is to visit the Hodoku site here.

You can download its puzzle generator/solver and I believe that you can create and solve puzzles of just about any level of difficulty. It also has a database of puzzles of various grades.

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Re: Where to find extreme(+) puzzles?

Postby eleven » Mon Sep 04, 2017 10:03 pm

One more remark:

If you want to solve the hardies manually, for sure the fastest method on average is nested guessing, i.e you guess something, and if you are stuck guess again. If it leads to a contradiction, you remember that and go back for the next alternative guess. If all ways lead to a contradiction you know that the original guess was wrong.

What you are guessing, can be different, the simplest strategy is to guess one of 2 possibilities, or - if not available - one of 3. And this is a good one.
Another one is to guess the solutions of a unit, where you select one, which has only few, say 6 or 7, if available. Here the ways to a contradiction will be shorter with a unit filled, at the cost of more starting guesses.

However the interesting part in such a solving is just in the selection of the guess, the rest is boring. So not many will like to do that manually.
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Re: Where to find extreme(+) puzzles?

Postby SpAce » Tue Sep 05, 2017 10:30 pm

Thanks, everyone! I'll be sure to check those resources.

I'd also like to clarify my current goals a little bit. Based on the answers I assume Sudoku Explainer is kind of a standard rating system here? I just let it grade a couple of those Nightmares I've completed and also the one I got stuck with (not a Nightmare). The Nightmares both got 7.2 (even though SudokuWiki graded them quite differently: 569 and 898), and the one that beat me got 8.4 (~1500 in SudoWiki). Based on that I guess my target level at this point is around 7.5 - 8.5. I don't want to depress myself by trying to jump too high at once :)

I also know that I still have a lot of work to do with even some pretty basic patterns. For example, I've never recognized a live WXYZ Wing as such, even though I've used them as parts of ALS chains unknowingly (and once as an ALS XY, which is also the only time I've spotted that pattern). I'm also terrible with fishes, of which I can only find basic types and sometimes finned and sashimi variants (I don't really like fishing anyway and often miss even basic Swordfishes unless I actually bother to look for them). I've never spotted a Sue-de-Coq or a Death Blossom (and only once a basic ALS XY), but they'd be fun to learn. I've never used APE either, but it doesn't really seem like an interesting or human-friendly technique to me anyway.

My main tool for the harder puzzles is AIC Nice Loops, and I'm getting pretty decent at spotting useful chains of various types, including grouped and ALS kind. They're fun to hunt, too, and so far they're been quite enough for the Nightmares. The one that beat me would have required some triple forcing chains, which I didn't even think of trying at the time (when I got and remained stuck, I thought I was just blind to some simpler pattern, but it wasn't the case). Had I thought about forcing chains, I might have had a shot at solving it, but I don't know.

Anyway, forcing chains and possibly nets are in the range I'm looking for, because my technique already supports spotting them (at least better than other patterns). Non-chaining patterns are more difficult for me and would require bigger adjustments to my manual technique (enhancing that is also a goal, however). Puzzles requiring Exocets, monster fishes or other exotic patterns aren't on my shopping list right now. I want to fully understand how and why a pattern works before I even try to use it, and currently I don't understand the inner workings of Exocet, for example (haven't much looked into it either).
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Re: Where to find extreme(+) puzzles?

Postby eleven » Wed Sep 06, 2017 8:48 pm

Nice, that you answer again, often people vanish after a response.

Some more points from my side:
I agree, that practicing ALS chains will make it superfluous to learn many kinds of wxyz-wings. Also many eliminations of Sue-de-Coqs can be found/expressed with ALS chains.
2 way forcing chains are logically equivalent to AIC's (or ALS chains).
The AIC freaks here call 3 or more way forcing chains Kraken (but the word is also used for extended fishing patterns).
Loops often give many eliminations, but seldom effectively advance the puzzle.
For very hard puzzles you will need a net, for even harder nested nets.

Maybe you want to post the hard nightmare, i wonder, how the programmers here would attack it.
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Re: Where to find extreme(+) puzzles?

Postby Leren » Thu Sep 07, 2017 9:53 am

You might like to try the puzzle posted today here.

Both solutions posted used non-linear chains, which sounds like the extra level of challenge you are looking for.

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Re: Where to find extreme(+) puzzles?

Postby SpAce » Fri Sep 08, 2017 12:52 am

eleven wrote:I agree, that practicing ALS chains will make it superfluous to learn many kinds of wxyz-wings. Also many eliminations of Sue-de-Coqs can be found/expressed with ALS chains.
2 way forcing chains are logically equivalent to AIC's (or ALS chains).


Thanks. That's pretty much what I suspected.

The AIC freaks here call 3 or more way forcing chains Kraken (but the word is also used for extended fishing patterns).


Interesting. I've only seen the word with fishes, but haven't really looked into it yet. Good to know it has another meaning, although I don't really like it when words have multiple meanings in the same context (seems to be a somewhat common problem in sudoku terminology, although I understand historical reasons for it).

Loops often give many eliminations, but seldom effectively advance the puzzle.


Yes, I've noticed. Most of the loops I find are discontinuous type 1 (weak-weak) which means it's pretty slow going. Then again, I don't really mind as long as some advancement happens and the hunting is fun.

For very hard puzzles you will need a net, for even harder nested nets.


I've gathered as much. My current last-resort method is a manual version of GEM which supports limited netting, but I don't think that would be nearly enough for harder puzzles. In the nightmare levels it's often very effective, almost to the point of feeling unfair, and that's why I only use it if I can't find other ways to advance (but if I do use it, I always find the logic behind the inferences it provides before taking advantage of them). I couldn't have solved my first few nightmares without it because I wasn't that good at spotting chains and stuff, but the last few I've managed to do without. However, I'd guess it's not that potent in much harder puzzles. First, its effectiveness depends on the selection of the seeding point (and my mark-up doesn't support more than one very well), and second, it's still a binary technique and wouldn't help with 3- or more way chains or nested nets, I guess. At least it didn't help me much with the one that beat me (then again, I only tried one seeding point).

Maybe you want to post the hard nightmare, i wonder, how the programmers here would attack it.


The one that beat me was not a Nightmare but the penultimate 3D Medusa example from SudokuWiki:

000900030004700600081054002005000000000020308000090060000070800017000000400106050
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Re: Where to find extreme(+) puzzles?

Postby SpAce » Fri Sep 08, 2017 1:00 am

Leren wrote:You might like to try the puzzle posted today here.

Both solutions posted used non-linear chains, which sounds like the extra level of challenge you are looking for.


Thanks! I'll try that during the weekend.

Edit: Okay, I solved it. A fun puzzle, but not very difficult. Seemed about the same as the nightmares, or maybe a bit easier as there were so many obvious chaining opportunities. Maybe I was lucky but I spotted immediately a continuous nice loop that gave 11 eliminations. After that a couple of discontinuous ones (I count 5 but I'm not sure if they were all necessary), some of them grouped, and it was smooth sailing. I also found some ALS loops and one non-linear loop, but didn't end up using them as I saw a basic one that ended up solving the rest. Looks like the most advanced technique I used was a grouped AIC.

Edit 2: Obviously my loopy way is far from efficient, by looking at the elegant one-step solutions posted. How do you get to that level? (I wasn't even aiming for a one-step solution as I didn't know it was the whole idea... probably wouldn't have happened anyway.)
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Re: Where to find extreme(+) puzzles?

Postby SpAce » Mon Sep 11, 2017 4:33 am

I reworked the 8.4 puzzle that beat me before and got it solved this time (not in a way that I would make me happy, though). I did it as far as I could normally, using loops and chains of varying complexity, but couldn't get any farther than the first time (7 cells solved). Probably got a few more eliminations, though, which might have made a difference. When I got frustrated enough I gave up and tried GEM again, even though it didn't help much last time. Now it solved the whole thing. I probably didn't apply it properly and/or had a poor seeding point the first time. It's not a very fulfilling way to solve, but it's easy and powerful if style points don't matter. I call it the Dark Side of the Force.
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Re: Where to find extreme(+) puzzles?

Postby David P Bird » Mon Sep 11, 2017 9:56 am

SpAce, as the originator of GEM, I admire your perseverance in employing it manually and am pleased that you have been able to benefit from it.

After a while the housekeeping involved in solving puzzles gets very tedious, so I designed a 'Sudoku Drudge' spreadsheet to highlight singles, doubles, etc so I could quickly get to the more challenging bits. I then extended its colouring capabilities to be able to follow alternating inference chains using the GEM equivalence marks.

The system allows all the bidirectional inferences that stem from a pair of seed nodes to be followed and this includes the various branches that exist. Where different branches converge on a cell, the marks may show if only one of the candidates can be true at one parity. However I discipline myself only to follow single, un-branched chains, so I do not grade-mark these candidates as that would amount to using a network approach.

Taken to completion, GEM marking will kill most published problems very easily, but will identify many insignificant eliminations in the process. Here the challenge is to firstly only to mark up the parts of a puzzle that appear to have openings and secondly try to keep the solution as short as possible by identifying and eliminating the significant candidates first. As the level of difficulty of the puzzles increases though, it becomes necessary to look for patterns such as Unique Rectangles and Finned Fish that will provide further inferences that can be followed.

Used in that way it need not be the 'Dark Side of the Force' that you are making it out!

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Re: Where to find extreme(+) puzzles?

Postby Leren » Mon Sep 11, 2017 11:22 am

I ran your hard puzzle through Hodoku and it's solution was a real nightmare. Among it's many moves were 18 linear AIC's and three Forcing Chain moves that read like War and Peace.

Well worth downloading this free software. If you are having trouble solving a puzzle, check the Hodoku solution, and if it's no simpler than yours you can stop beating yourself up trying to find an easy solution that is just not there.

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