Help! I want to see a REALLY HARD SuDoKu puzzle

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Help! I want to see a REALLY HARD SuDoKu puzzle

Postby Guest » Wed Jun 01, 2005 3:39 pm

I have tried Sudoku puzzles that rated themselves as easy, medium and hard. I didn't find the "hard" at all hard; they just took a little longer. Can anyone steer me to some really hard puzzles? The ones I have looked at so far have easily fallen to the 3 or 4 step process I developeded in solving the two "easy" ones.

I would love to find something solvable but hard.

TIA,

B. King
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Re: Help! I want to see a REALLY HARD SuDoKu puzzle

Postby scrose » Wed Jun 01, 2005 4:17 pm

Try some puzzles that require the swordfish technique. Or try the samurai sudoku from this past weekend. Or try the dion cube from a couple weeks ago.

(updated: mentioned dion cube)
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Postby abailes » Sat Jun 04, 2005 7:32 am

I remain unconvinced that there is not some cunning logic that will allow this one to be solved without trial and error

http://forum.enjoysudoku.com/viewtopic.php?t=387
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Postby Animator » Sat Jun 04, 2005 11:06 am

First, how many Hard-puzzles did you try? the difficulty is different between Hard puzzles aswell... some are harder, some are easier... so I suggest you try some more, and when you are done with that, you should try some Very Hard puzzles...
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Postby Francisco » Thu Jun 09, 2005 3:45 pm

abailes wrote:I remain unconvinced that there is not some cunning logic that will allow this one to be solved without trial and error

http://forum.enjoysudoku.com/viewtopic.php?t=387


I solved that a few days ago.

It takes "Trial and Error". But Trial and error is still a logic step (ONLY a very ELABORATE ONE:) ).

It's like you thinking in your mind what would happen if you chose number a instead of number b for a certain position...

So "trial and error" is LOGICAL... so use it when the puzzles get to tough
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Postby lobby__boy » Thu Jun 09, 2005 4:06 pm

in a sense, trial and error is just a more complex logical step. the thought process for a lot of su doku moves is something to the order of "if this goes here, then it conflicts with *other number placement*. ergo, this cannot go here."
we even go to the trouble of pencil marking it. trial and error just adds intermediate steps between the 'if' and the 'then', so it's actually a chain of 'if this.....then......then.....then....then *conflict*: thus: conclusion' it's a longer induction, but of the same sort.
wow...we americans are long winded.
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Postby abailes » Thu Jun 09, 2005 4:09 pm

Francisco,

I'm inclined to agree with you, but that won't make us very popular on these forums. Although, I have to say that I have stopped using T&E since I started posting in the last couple of weeks or so. I can see both sides of the argument.

I think the biggest argument for frowning / disallowing T&E is that some puzzles that are logically very difficult can be solved more quickly by a human solver with T&E than by using the logical path. That is a shame as there is a certain beauty in knowing that you have solved the puzzle the way that its creator intended. Particularly if you are given puzzles, like the Pappocom puzzles, that you know don't need it. I'm not sure how they are going to police T&E (or whether they should try) in the upcoming tournaments.

I also agree that some forms of T&E are very similar to some of the advanced forms of logic. Particularly if you don't quite get the rules for xwings and swordfish, you can prove to yourself how they work by using T&E.

This puzzle I posted is a classic example as you get very close to the end before you seem to need T&E. It is just so tempting to use it and ignore the puzzle rather than keeping it alive in the hope that it will open up some other clever form of logical solution. If I remember correctly, there is a simple T&E solution that quickly solves itself - i.e. within 5 cells or so - in the top left corner. Does this become some form of advanced logic, or is it just cheating? Does it only become logic if you can generalise the rule (like xwing or swordfish)?

Maybe we should kick off a different forum for this discussion.
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Postby abailes » Thu Jun 09, 2005 4:10 pm

Lobby_boy - looking at the length of my reply, not as long winded as us Brits, it appears...
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Postby george-no1 » Fri Jun 10, 2005 4:12 pm

abailes wrote:I'm inclined to agree with you, but that won't make us very popular on these forums.


It makes you popular with me, that's what I've thought all along! When it comes down to it, quite a lot of 'techniques' are just a watered-down version of trial and error. When I started, I simply used what I thought was trial and error, but I now realise the things I was doing are actually proper 'techniques'. However, calling them techniques doesn't mean they stop being a form of trial and error!

Although, I have certain limits in the forms of trial and error that I use, as I'm sure most other people do. For instance, I limit myself to pencilmarks only on Difficults and Fiendishes, and I have never simply copied out the grid on the base of a guess out of two possible numbers, or anything like that. It is my opinion that Trial and Error is fine to use, and in most circumstances unavioidable - what I find unacceptable (myself) is guesswork. I think this may be the point that have being trying to get at.

George:)
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Postby martinji » Sat Jun 18, 2005 10:40 am

abailes wrote:Francisco,
I'm not sure how they are going to police T&E (or whether they should try) in the upcoming tournaments.


IMO, no way should T&E be prevented (and I very much doubt it will). I'm in the Independent's regional final next saturday and even though I've never used T&E I support its use as a valid technique. I may even have to use it myself next week if I think it will be quicker.
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Re: Help! I want to see a REALLY HARD SuDoKu puzzle

Postby JOTHI » Mon Jun 20, 2005 2:25 pm

bking43 wrote:I have tried Sudoku puzzles that rated themselves as easy, medium and hard. I didn't find the "hard" at all hard; they just took a little longer. Can anyone steer me to some really hard puzzles? The ones I have looked at so far have easily fallen to the 3 or 4 step process I developeded in solving the two "easy" ones.

I would love to find something solvable but hard.

TIA,

B. King



HI sir ,

This is from an INDIAN . Do you want to solve sudoku of order 100 by 100 (or more).pls mail me at mailtojothi@gmail.com
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Re: Help! I want to see a REALLY HARD SuDoKu puzzle

Postby Wolfgang » Wed Jun 22, 2005 12:21 pm

bking43 wrote:...
I would love to find something solvable but hard.
...
B. King


Here are the 2 hardest my program found so far:

0 9 0 0 0 0 0 0 0
6 4 0 0 0 0 0 9 0
0 0 0 0 3 0 4 0 0
0 0 0 7 0 0 3 4 0
0 0 7 0 9 0 5 0 2
0 0 0 0 0 2 0 0 0
0 0 5 0 1 0 0 0 0
0 7 9 0 8 0 0 0 1
0 0 0 0 0 0 7 6 0

0 0 9 0 7 0 0 8 0
0 0 8 0 0 6 0 0 0
0 0 0 8 0 0 6 0 5
0 0 3 0 0 2 0 5 0
0 0 7 6 0 0 0 0 0
1 0 0 0 0 5 0 0 9
0 4 0 0 0 0 0 9 2
7 0 0 0 0 0 0 0 3
9 0 0 0 1 0 5 0 0

br
wolfgang
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Postby scrose » Wed Jun 22, 2005 1:56 pm

Wolfgang, are you sure you typed in your second puzzle correctly? I was able to fill only one cell (r2c7) before I had to use trial-and-error. The puzzle does, however, have a unique solution.
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Postby Wolfgang » Wed Jun 22, 2005 4:28 pm

scrose wrote:Wolfgang, are you sure you typed in your second puzzle correctly? I was able to fill only one cell (r2c7) before I had to use trial-and-error...

oh, i did not not claim that you can solve it without using t&e, only that it is really hard, like bking43 it wished. I am sorry when someone thought that the known techniques like swordfish etc. would be enough to solve it.
Of course, if you use t&e to try one number and after ten steps you see that this is not possible, you can also call this a technique. But i dont want to start a discussion about that again ...
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Postby scrose » Wed Jun 22, 2005 4:47 pm

Wolfgang wrote:you can also call this a technique

But is it an enjoyable technique? Personally, I don't derive pleasure from having to retrace my steps after making an incorrect guess. I will agree with you that the puzzle is hard, but I would not enjoy solving it. But I suppose you can say that you never claimed the puzzle would be enjoyable...:)
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