The New Sudoku Players' Forum

[EssJay]

I have just learned from our administrator that a similar puzzle in the Telegraph expects puzzlists to use trial-and-error (T&E). Gasp!!? Am I alone in having to resort to T&E with The Times 'fiendish' puzzles? I've never yet managed to complete one without doing so. Presumably I will eventually learn to recognise when a clue is staring me in the face?

A rather frustrated (but getting there) EssJay

[Chris]

I think that The Telegraph's trial and error strategy is quite bizzare. The only way you can really engage in a trial and error strategy is when you have more than one grid to try each method and see which work. As you only get one copy of the grid in the newspaper then you could totally screw it up by following the wrong path, so to speak. It isn't even like one can use a pencil to fill the grid in as pencils are so hard to write with on newspaper.

[dkintheuk]

But...

IF you do end up using trial and error - as i have had to with fiendish puzzles too - there are a variety of stratefies to enable to try things out.

I use Excel to draw up the grid so i can use undo to step back where i have tried something out.

You could use pencil on a newspaper but, i would advise a click style pencil that has a fixed width of lead so as to keep your text nice and small with ease.

Also you could very easily make up a blank grid template and wither print or copy a lot of pages to keep you busy.

Having said that i intend to get away from the T&E method ASAP. I just get stuck every now and again.

One final note - I find that if i use the T&E method, i end up making more mistakes that i would without it.

Good luck to all,

Rob.

[Chris]

But...

IF you do end up using trial and error - as i have had to with fiendish puzzles too - there are a variety of stratefies to enable to try things out.

I use Excel to draw up the grid so i can use undo to step back where i have tried something out.

You could use pencil on a newspaper but, i would advise a click style pencil that has a fixed width of lead so as to keep your text nice and small with ease.

Also you could very easily make up a blank grid template and wither print or copy a lot of pages to keep you busy.

Having said that i intend to get away from the T&E method ASAP. I just get stuck every now and again.

One final note - I find that if i use the T&E method, i end up making more mistakes that i would without it.

Good luck to all,

Rob.

They are all great methods (although I'd recommend using the excellent Su Doku program available for download on the main page) but they aren't things you can do on the train every morning on your way to work. I think the idea of having a Su Doku in the newspaper should be that it can be done without recourse to any other utilities and can be completed on that page with just a pen/pencil. If The Telegraph want people to solve the puzzles using trial and error then I think they should really print multiple grids in their newspaper. Not that it matters to me that much as I'd never switch from the Times, but it just seems baffling.

[Buildyperson]

I think all su doku puzzles should be solvable without recourse to Trial and Error. The fiendish Times puzzles stretch this belief to the limit, but with perseverence they can be solved using logic alone and a careful check and re-check of the information available.
I have been tempted to use Trial and Error, but as noted above, this is not convenient when using a pencil and a newspaper, and in my opinion,is not as satisfying.

[Guest]

I just write down all the possibilities in each box and cross/ rub out those that I eliminate as I go along. I agree that a click pencil is most suitable for doing it on the paper.

In excel, i made a grid and locked the cells that are given to start with (a complication that need not be done - too much effort for a normal computer user).

It's tempting to create a program to solve the puzzles but that would be boring and there'd be no point.

enjoy your puzzling

wyrd

[Guest]

Is it confirmed that the Torygraph's puzzles are Trial and Error?

Was this written down anywhere? I've been doing the Telegraph puzzles and have so far failed to complete a medium type one (But I think that was because it was the third one that I'd done) and the 'diabolical' on on Friday.

I've been using the 'carpet bomb' approach with some success, but may rethink.

So far my solving routine goes something along the lines of

fill in all available numbers in all squares.

Eliminate any obvious ones where there's only one possible number in a square.

Run through Rows checking to see if there's only a single number anywhere on a row.

Ditto with columns.

Ditto with 3by 3 squares.

Eliminate any surplus numbers (like when you end up with two squares with two possible numbers in) thus combining a number to a specific row or column.

rinse and repeat.

Are there any other tricks I'm missing?

I like to do these on the train, but if there's a possibility that I'm going to have to be reduced to trial and error, then I'm not going to bother any more.

[Guest]

I must agree that trial & error is not a proper option for solving these puzzles. If the puzzle is not soluble by calculation, then it should say so and save me the trouble!

[Guest]

I'm a bit of a newbie to Sudoku (rapidly getting hooked). But its strikes me that a form of "Trial & Error" is actually a valid logical technique - I'm referring to the technique of "proof by contradiction". To establish a conclusion you assume the opposite and persue the rules of logical inference, until you come to a self-contradiction. Hence you deduce that your original assumption must have been wrong. The best known example is probably the proof that the square root of 2 is irrational.

I can't see anything wrong in proniple in having to resort to this type of technique to solve Sudoku: Given, say, two squares where a "7" can go, try one and see if a self-contradictory position results.

I would guess that the main headache with this approach is that it is hard to carry too much data in your head. You don't want to fill in numbers you're not certain of, so you have to keep them in your head. A bit, I suppose, like planning ahead in chess. I'd certainly find this hard going if th solution didn't emerge fairly quickly.

The telegraph Sudoku web site says that their Tough and Diabolical puzzles need a "bifurcation" (as they call it in one place - i.e. you need to guess one route and see where it leads); but they will never need a second bifurcation later on.

[Guest]

I found one of the Times' ones a few weeks ago that I couldn't solve (Friday, surprise, surprise), so I decided to take a stab as to which of 2 possibles should go in a square that I was sure would unlock the puzzle. I do the Difficult/Fiendish ones in an Excel grid, so I can undo... I set all the squares I had not filled in to red font and carried on. It came out straight away. Just for grins, I deleted all the red numbers and tried the other number... It came out again! Since then, I've seen 2 or 3 that come out in 2 or more possible ways.

It doesn't always happen, of course, but I have to wonder whether the checkers for the competitions always check that a valid solution has been provided, rather than just comparing with their own one?

[Administrator: See the Solving Techniques forum ("Solving with Excel") for a continuation of the Excel discussion]

[Guest]

essjay if you have the right techniques then you do not need trial and error for the times one. e.g if there 3 squres in which thre numbers only will fit then the same numbersin the row/column or box can be eliminated

[Guest]

Now that's an elegant technique... I like that one... a lot :D