The New Sudoku Players' Forum

[Christianbuus]

Hi you guys

I have a question: In my online sudoku solver, I´ve applied the "hidden subset" technique, but though it works perfectly, it´s never used to solve sudokus. Therefore, my question is, is the "hidden subset" technique actually a necessary technique to solve certain sudokus?

The techniques I´ve also applied, which I think may "substitute" the "hidden" technique are: Naked Single, Hidden Single, Block and Column / Row Interactions, Disjoint Subsets (from 2 to 8 integers which are "connected" in the same amount of connected cells), X-wing, Swordfish, Jellyfish, Squirmbag (again checking up to 8 rows / columns), and XY-chains (golden chains, I used link at krazydad.com).
My solver checks for the techniques in the above order. (Actually it checks for hidden subsets before the XY-chains, but I don´t think it matters).

So do any of you guys know if the hidden subset technique is just a technique that is easier to spot for the human solver but not necessary, and therefore can be removed from my solver?



Thanks,
Christian


P.S. The solver is currently "talking" danish, but I´m working on a english version, and adding new techniques. If you want the solver to illustrate the different techniues used to solve the sudoku, push the second button "Spring nemme led over".

[aeb]

In my online sudoku solver, I´ve applied the "hidden subset" technique, but though it works perfectly, it´s never used to solve sudokus. Therefore, my question is, is the "hidden subset" technique actually a necessary technique to solve certain sudokus? The techniques I´ve also applied, which I think may "substitute" the "hidden" technique are: Naked Single, Hidden Single, Disjoint Subsets (from 2 to 8 integers which are "connected" in the same amount of connected cells).

It sounds like your Disjoint Subsets do the job.
Naked subset: you find n positions where only n digits can occur. Hidden subset: you find n digits that together can occur in only n positions. Whenever you have a hidden subset of size n, its complement is a naked subset of size 9-n. So one does not need hidden sets, naked sets suffice.
Or, one does not need naked sets, hidden suffice. Or, one does not need sets of size 5 or larger, sets of size at most 4 suffice. Pick whatever you like best. I think most people like this last version, and avoid large sets.

[Jeff]

Actually it checks for hidden subsets before the XY-chains, but I don´t think it matters).

So do any of you guys know if the hidden subset technique is just a technique that is easier to spot for the human solver but not necessary, and therefore can be removed from my solver?

Hi Christianbuus, For any hidden subset, there is a corresponding naked subset. I guess your solver checks naked subsets before hidden subsets and this is why the hidden subset is never get used. Try to reverse the order and see if it does make an inpact.

You are right; it doesn't matter if the solver checks for hidden subsets before the XY-chains; which should have nothing to do with the requirement of hidden subsets.