Hey
As the competition is over now I wanna ask about the 6th sudoku, the 60 point classic one. Was it only possible to solve it using so-called 50-50 method (randomly trying one of two possibilities) and not logically? I managed to solve first 5 sudokus without problems but in this one I had to use 50-50 twice to get it solved (luckily still managed it on time)...
Cheers,
driv4r
Why is this a problem?
Why is what you are calling the "50-50 method" not an acceptable method to require in a puzzle? Every step in a logic puzzle such as sudoku is a use of the "50-50 method," since the number you are placing could go in any of up to nine different spots, but all but one of them leads to a dead end. Any techniques that people develop/use for solving puzzles are basically just shortcuts to lessen the effort required to confirm or deny that something goes in a particular spot (often by decreasing the number of steps it takes to reach a dead end). As long as a puzzle has a unique solution though, it can be solved "logically."
on guessing
Clearly a lot of solvers have an idea of "logically solvable" that is not equivalent to "has a unique solution". See http://www.gmpuzzles.com/blog/2013/03/ask-dr-sudoku-12-the-line-must-be-... or http://puzzling.stackexchange.com/questions/12/are-there-sudoku-puzzles-... for some discussion.
That said, while I didn't solve the 60 pointer during the test, I did afterwards, and it didn't feel like "unsolvable", though I can't say I remember the solving path exactly.
It wasn't too difficult...
It wasn't too difficult... one X-wing and one XY-chain (my preferred method) and its done.
On guessing and sudoku itself...
Yes, as rob said, by saying it wasn't logically solvable I didn't mean that it didn't have a unique solution, you kinda missed my point or only partly understood me ghirsch.
What I meant by the "50-50 method" is that to fill a particular cell the only way is to guess i.e to try 1 of 2 options (if it's wrong try the other one) and that there is no other logical way to decide, which option (number) is correct.
And I didn't say that it's not an acceptable method, though I do admit that I would prefer not to have those in competitions.
Anyway, as I understood, it was actually possible to solve this one without guessing, so those that did solve it logically, care to explain how?
As I said, I got it solved myself but only thanks to guessing twice, so it would be good to know how to properly solve it...
You can see lot of methods
You can see lot of methods explained here: http://www.sudokuwiki.org/sudoku.htm The difficulty ordering is personal preference; for me it is easier to find and use XY-chain (= Y-wing for 3 cells) and Unique Rectangle rather than X-wing...