Sudoku Players' Forum (clone)

Q. What's the simplest way to identify that a grid has multiple solutions?

This isn't a test - I just want to know how I can ensure that grids are unique before wasting time on fruitless endeavours! (I'm talking about the logic and structure - not bunging the grid into a solver and seeing what it says! )

stuartn

I don't know if there IS a way to tell, without trying to DO the puzzle and getting stuck because there's no "logic next step" - but that COULD mean the puzzle has multiple solutions, or just that you need a technique you're not familiar with, or that there's something blindingly obvious that you're missing (have had my share of those!)

The easiest way is to pop it into one of the programs - Pappocom Sudoku will tell you if it's a valid puzzle (unique solution) without showing you the completed grid.

I think of a grid as a the complete 9 X 9 filled with the appropriate numbers/symbols in accord with the Sudoku rule. In other words, a finished puzzle. I would also think that generating said (grid) would be the first step in creating a puzzle. The second step being the designation of clues that will for the most part determine the degree of difficulty, and ensure a unique solution. It's not that a (grid) has more than one solution then, but that either the clues or the logic needed to extend them to completion are lacking.

So I don't know how you could spot a multiple solution puzzle without some sort of comprehensive examination that in effect solves the puzzle.

What is the correct term for the (grid) I describe?

cho

Shazbot wrote:The easiest way is to pop it into one of the programs - Pappocom Sudoku will tell you if it's a valid puzzle (unique solution) without showing you the completed grid.

Actually, that's the one program *not* to use, as it does not distinguish between malformed puzzles with no solution, those with multiple solutions and perfectly good puzzles with unique solutions that require logical means beyond its scope. It will choke on them and claim they are INVALID. A great many of the puzzles discussed here cannot be loaded into Pappocom software.

tso wrote:Actually, that's the one program *not* to use

Oops - thanks for that warning. The only programs I have are Pappocom and Simple Sudoku. I've seen others mentioned but really didn't see a need for 10 programs for the same "game". What do you recommend (maybe that's another thread)?

I think that choke is hyperbolical – I'd say it's more like Pappocom has a taste of those other puzzles and spits them out.

To be fair, Shazbot, not everyone agrees with tso that Pappocom should validate other puzzles. Its program is designed to create puzzles that are do-able on paper without the use of advanced techniques (nothing harder than Xwing) and those are the puzzles that it validates. Anyone who wants to do the more difficult kind can use a different program.

That said … there’s no doubt that Pappocom has less appeal to more advanced solvers because of the restrictions it places on itself.

This topic has been split at this point. The remainder of the original topic is now in the "Solver programs" forum. Future posters in this topic should follow whichever aspect of the thread they are interested in.

- Wayne