JPF wrote:The best way to define a rating system for the difficulty of sudoku puzzles close to the difficulty felt by humans is to set-up an ad-hoc committee of human solvers. The committee would solve all the puzzles submitted to them. The average time taken by the committee to solve the puzzle would by definition be the rating of the puzzle, measured in seconds.
To avoid that the growing competence of the members of the committee leads to a bias compared to amateurs, it would be advisable to renew each year a part, say 50%, of the committee...
SpAce wrote:Even if a puzzle took a long time to solve because of many required steps, I wouldn't call it difficult if it could be progressed relatively constantly. A puzzle could also take a long time just because it has a narrow and non-obvious solve path, even if relatively few and easy techniques are actually required. (The latter case is a bit more related to actual difficulty.) Personally I think the most interesting rating is simply based on the hardest step required (like SER but with updated techniques and ratings), though it's obviously not the whole story.
Hajime wrote:Where can I find info about 'Ruud's rating system'?...
mith wrote:For clarification: minlex isn't a rating. It's a way of choosing a "canonical" form of a puzzle (which is useful for determining if two puzzles are isomorphic).
Pupp wrote:Ahh, ok. I have no idea what a "canonical" form of a puzzle is, or what it means for puzzles to be "isomorphic".
Mathimagics wrote:Pupp wrote:Ahh, ok. I have no idea what a "canonical" form of a puzzle is, or what it means for puzzles to be "isomorphic".
Two solution grids are isomorphic (aka "equivalent") if one can be transformed to the other by a set of standard operations (eg reordering the bands).
If two grids are NOT isomorphic, we say they are essentially different, or "ED".
There are 6,670,903,752,021,072,936,960 different solution Sudoku grids, but structurally there are only 5,472,730,538 essentially different grids.
Because there are so many isomorphisms, for analytical purposes we like to deal with a canonical form, this just means a standard representative of all the grids that are isomorphic to any particular one. If you sorted the full set then chose the first grid in the sorted list, that is a good choice - that is called the minlex grid (lexicographically minimal representative).
See: Wiki - Mathematics of Sudoku for a description of all the 3,359,232 x 362,880 ways that grids can be isomorphic.