Sudoku over time ..

[Cyril Haearn]

I recently started doing sudoku, not sure if I love it or hate it. Sometimes I can get many numbers, then it gets harder when the grid is more than half full. Anybody been doing it for longer, does one get bored and lose interest?

[661-Pete]

I've been doing them daily over quite a number of years now, mostly the one in the Grauniad - and I flatter myself I almost always solve them . It's a good way of keeping the old grey matter in circulation and, hopefully, staving off Alzheimer's or the like. In the Graun they have a habit of making them progressively harder through the week - Monday's is classed as 'easy' whilst Friday's and Saturday's are usually described as 'hard'. Though I don't always find these categorisations very accurate.

I always use pen and paper to work through the Sudoku - never resort to any computer-aided apps.

Another feature of the Graun's is that the pattern of clued squares versus non-clued squares, is always symmetrical. This may lead to some of their puzzles being easier than they need to be. Though their 'hard' ones can certainly be tough!

I believe it has been mathematically proven that the minimum number of clues for a solvable Sudoku is 17 - though I'm sure that if I read the proof, I wouldn't understand it...

[Cyril Haearn]

17 the minimum, or none at all? - maybe that would be a good challenge, not soo easy?

[peetee]

Not my fave puzzle.
I like them when they are easy but don't really enjoy the hard ones.
Overall I would give them 1 to 9.

[661-Pete]

This is reckoned to be one of the hardest. Not symmetrical, therefore not from the Grauniad - too tough for them I think! I've not done it yet. Have fun!

hardest sudoku copy.jpg (20.29 KiB) Viewed 2673 times

[peetee]

Call me a bike obsessive if you will but on completion of a sudoku I can't resist trying to find 531, 653, 753 etc in the grid.

[freeflow]

Soduku are just a set of simultaneous equations. As such they are all easy peasy.

[661-Pete]

Soduku are just a set of simultaneous equations. As such they are all easy peasy.

Don't know about that. A sudoku solution is independent of any permutation of the numbers involved - and it is possible for the matrix to be singular (determinant = 0) - which would make any attempt to solve simultaneous equations rather hard! See here.

[Tangled Metal]

I've played a few sudoku apps on my tablet and phone. I usually start with an easy then work my way up through the grades then once I've completed one out of each grade i go back to hard and treat it as a speed challenge. Each puzzle needs to be completed quicker than the previous. Not always achievable but it adds a bit off fun. Currently 2m53s for a hard puzzle. Subjective because that I one just fell into place a lot easier than some easy ones.

My only issue with sudoku is that I'm running out of apps for it on Android! I'm close to repeating previous apps.

There have only been 2 puzzles I've not completed. Both hard category on one Android app. The reason it's not done is because puritanically i won't guess at any point of a puzzle. Those 2 i reached a point my logic skills could not progress. A guess between two numbers that are linked for two cells is not completing it IMHO. Say one cell could be a 1 or 8, another cell could only be a 1 If the first was an 8. I basically had a 50:50 chance of guessing right but i could not see any way of logically working it out. At that point I'll move on or reset it.

BTW there have been sudoku puzzles in quality newspapers in pull out sections that i had no idea of how to complete them. Killer sudoku is the name IIRC and they've got missing numbers or other tricks. Things like lines around numbers in adjacent 9 cell blocks. As well as usual rules you have to put one number 1-9 in these lines. Added difficulties that i just don't enjoy.

[661-Pete]

I don't bother with 'killer' sudoku - the standard variety is sufficient grey-matter exercise for me! There are 'Killers' regularly in the Grauniad: appear to have an extra layer of artificiality put on, don't really appeal to me.

The reason it's not done is because puritanically i won't guess at any point of a puzzle. Those 2 i reached a point my logic skills could not progress. A guess between two numbers that are linked for two cells is not completing it IMHO. Say one cell could be a 1 or 8, another cell could only be a 1 If the first was an 8. I basically had a 50:50 chance of guessing right but i could not see any way of logically working it out. At that point I'll move on or reset it.

Perhaps we are at odds as to what exactly we mean by the word 'guess'.

I'm not a chess player and I don't have the skill to be able to look too many moves ahead. Quite often I can, nevertheless, complete a sudoku simply by looking for forced placements (cells where only one digit will fit, or rows/columns/boxes where a specific digit will only go in one cell).

But sometimes I get to a point: I'll prefer to call it a 'branch' or 'bifurcation' rather than a 'guess', where I have two options for a particular placement, and I can't see enough moves ahead to tell which is the right one. Then I'll try out one of the two options, chosen at random, and proceed, writing in small digits, until I either complete the puzzle or reach a contradiction. If the latter, then I know I should have taken the other branch, so I cross out all the small digits and backtrack.

If however I complete the puzzle on the first branch, although I have the satisfaction of having solved the puzzle, there is the downside that I haven't proved that the solution is unique. Ideally I should go back to the branch point and try out the other branch, so as to prove that it doesn't solve. I'm usually too lazy to do this!

Occasionally, with a very tough puzzle, there may be two or more 'branches'. All adds to the challenge!

[Tangled Metal]

I used to be better at sudoku. Now i struggle to think much more than 3 moves ahead in 3 variations. I'm useless at chess but numbers suit me better for some reason.

Fiendish sudoku! Try one. I see no point in them i often can't get much more than one move in!

I don't seem to remember guardian sudoku being that hard. I used to get the newspaper as a student cheaply i think when they first started doing them. IIRC when certain broadsheet newspapers did a pull out puzzle booklet the sudoku in them went from very easy to "is that even possible, where are the numbers?"

[Mick F]

Once I sorted it out in my head and realised that all you need to do is go through all the permutations, it's easy ............. just longwinded.

The last one I did ............. and it's years ago ................ I used my computer to fill in all the permutations in the squares.

[661-Pete]

Once I sorted it out in my head and realised that all you need to do is go through all the permutations, it's easy ............. just longwinded.

What! All 6,670,903,752,021,072,936,960 of them?

[Mick F]

From what I remember, each line of three adds up to ten or something.
You do it in sections and/or lines ........... or that's the way I remember it. You don't do the whole puzzle in one go.
Can't honestly remember, and I'm not interested enough to work it out again.

It reminded me of cracking a basic combination bike lock. Start at all zeros, and move one end through zero to nine whilst pulling on the chain. You feel it "give" when the correct number is found. Then you go onto the second tumbler, and then third, then fourth. Maybe ten minutes maximum, and the lock is open.
This one, for instance.
http://www.halfords.com/cycling/bike-lo ... ombination

One bit at a time. You get a feel for it and know when one section is correct.

[Cyril Haearn]

Soduku are just a set of simultaneous equations. As such they are all easy peasy.

Don't know about that. A sudoku solution is independent of any permutation of the numbers involved - and it is possible for the matrix to be singular (determinant = 0) - which would make any attempt to solve simultaneous equations rather hard! See here.

Guten Tag Pete

Ich wuerde gern eine Uebersetzung deiner Unterschrift lesen, vielleicht eine englische?

Diolch yn fawr