The New Sudoku Players' Forum

[cphuntington97]

I've read that guessing is cheating.

If I have a square (1/81) with only 2 possible numbers, and I "guess" one and follow through to look for conflicts, and upon finding a conflict, know the other number must be correct - is this legitimate technique? Or is this "guessing?"

[Crazy Girl]

there are such things known as chains, where one looks at a cell with 2 or 3 possible values, say {1,2,3} in cell Row9 Column9, assumes the cell takes the value 2, and complete the puzzle until it leads to a dead end, or a contradiction, in which case 2 can be removed from the possible values from this cell. [obviously if 2 completes the puzzle then you guessed right ]

If you look through the forum (or use the search button above) you will find lots of posts explaining chains better than i can : and sometimes in too much detail to get your head around


Any puzzle by Pappocom does not require this, and the puzzle can be solved by logic alone. If you are stuck post your puzzle here, and someone will get back to you on the next step to take.

[emm]

People have different ideas about the meaning of the term guessing and a whole lot has been written about the rights and wrongs of it. I think that generally we say that puzzles that have more than one solution require guessing as there will be places with more than one option. For this reason guessing usually has a negative connotation.

To me guessing also implies that the person solving the puzzle is happy to accept any candidate because it works - without caring too much about understanding why or if it’s the only answer.

What you seem to be talking about is one form of trialling - testing a candidate in a logical series of steps to see if it works. Puzzles with one solution can be solved by a variety of trialling techniques, including randomly selecting this or that candidate and giving it a go. The chains that Crazy Girl mentions are a pretty obvious example of trialling in an advanced solving technique, but even a quick flash round the brain cells to determine the last clue in a row involves trialling in the sense that it’s checking the viability of this number in this place as against other numbers and other places.

A quick inference like this or recognising say, a hidden pair, certainly doesn’t feel like trialling. All the examples of hidden pairs or whatever that we’ve done up till now, have imprinted the pattern into our brains so that we can choose the right candidate without going through all the working out. We recognise the pattern rather than the logic behind it. It has been said that we’re no longer trialling when it’s automatic. Perhaps we could call it ‘intuiting’ - but the trialling process is an integral part of the pattern we recognised in the first place.

This has become a very long-winded reply, hope you haven’t nodded off.

Personally I don’t like the technique you’re talking about - trialling candidates until you reach a dead end, backtracking and starting again with another number. To me that’s boring and tedious and if that was the only way to solve Sudoku I wouldn’t do it.

What I find most satisfying is learning to understand and recognise the techniques and patterns that eliminate numbers without a lot of trialling. That to me is the challenging and rewarding part – even more than finding the solution. However it’s a personal thing – it’s a game after all, and we need to look for whatever makes it fun for us.

[tso]

No guessing is required to solve any logic puzzle, Pappocom or otherwise. The fact that the solution might be obtained more quickly by guessing doesn't change the fact that it's a mathematical construct -- given enough time, study and grey matter, they can all be solved by logic. There are plenty of puzzle that are difficult enough that they will stump many or even most solvers and we've all be stumped one time or another.

You're new here so this rant is not aimed at you: Why does this question get asked over and over and over and over? This is such a curious phenomenon -- and I know I've said this before -- but I've solved hundreds of different types of logic puzzles over the years and I've NEVER heard of anyone questioning if one could be solve by logic alone rather than require guessing -- the question has no meaning. It's like asking if there is a sequence of digits that is so long that it cannot be memorized. Yes, we can claim that no one can commit a trillion digits of PI to memory, just as we could certainly create a 10000x10000 Sudoku that no human could solve. But I *did* memorize PI to 500 digits in high school -- and the current record is at least 83,431. Where do we draw the line between possible and impossible? We don't.

[9X9]

CPH

The "guessing" you describe will never be necessary if you are doing either a puzzle generated by the Pappocom program or a Pappocom-originated puzzle such as those in the Times and Sunday Times. They are all solvable using the techniques set out in www.angusj.com. There is some additional information at www.simes.clara.co.uk.

Most players meet your type of "guessing" situation early in their sudoku lives, because their technical armoury is deficient, I certainly did and angusj.com remedied the problem. I now solve a couple or more of Pappocom Very Hards (Times Superior) every day with no recourse to anything other than the angus techniques, albeit expanded in a couple of places in the light of my own solving experience.

[Lummox JR]

To me guessing also implies that the person solving the puzzle is happy to accept any candidate because it works - without caring too much about understanding why or if it’s the only answer.

Exactly. To try something and seek contradictions is a form of trial and error, a logical test.

However, T&E is truly the last resort. If you can find a solution with any other logic technique, by all means do so.

[emm]

Why does this question get asked over and over and over and over? This is such a curious phenomenon

Yes, it is intriguing that 'Guessing/ T&E' comes up so often – it was the very first question ever posted on this forum and it’s popped up innumerable times since - but I think it’s quite understandable.

Most of us haven’t been doing logic puzzles all our lives, most of us had never heard of Sudoku a year ago and most of us quickly and frequently came across puzzles that stumped us. To me, Do I have to guess? is a perfectly natural response for people doing logic puzzles for the first time, especially ones they're having trouble with.

I don’t think the question is meaningless either in the What is possible? sense. If I’m not very good at chess I’ll get to a point where I don’t know what to do and I’ll have to make a guess about my next move, knowing that my more experienced partner can probably see the logical path to my downfall step-by-step. So, similarly, perhaps the answer is – No, you don’t have to guess, but you may have to if you don’t know what else to do.

What I find more curious is the way I’m always tempted to respond to the T&E issue. I mean if someone kept posting How Many Grids? - and they do - I wouldn’t feel the urge at all - but every time I see the word ‘guess’ I feel the anticipatory thrill of a minor feeding frenzy. Well, less so now – but it used to be like throwing a piece of raw meat into a sea of barracuda. I’m sure that’s because of the ongoing confusion over terms, it keeps it interesting – but that’s another matter.