Almost all Sudoku (or Number Place) puzzles are computer generated and computer verified. A Google search will give you a number of sites that will generate and solve puzzles for you. The notable exception is Japan, where most all puzzles are designed by hand and conform to stylistic guidelines, such as rotational symmetry of the clue number placement. The puzzles come in a wide range of complexity. Some can be solved with just a handful of solving rules. And I have seen some that the best solvers in the world cannot solver without resorting to extensive trial and error (essentially brute force). I'd be curious to see what the LA Times calls "daibolical"; please send me the clues via email. Difficulty would be hard to determine by a brute force solver. I image that they are rated by human test solvers, or a program that uses a range of solving rules and rates the level of complexity reached during the heuristic search. Those that appear in the U.S. Puzzle Championship (wpc.puzzles.com) are all designed by hand and are variations on the theme (since many of us have been doing Number Place for 10+ years and are somewhat tired of the standard style). For example this year we had one on a torus, with the 3x3 regions replaced by shapes that wrapped around one or two edges of the grid; and one with the number clues given as partial LED readout. Nick Dave Dyer wrote:
The sudoku puzzles that the L.A. times has started carrying have me wondering how the puzzles are created and validated, and especially how it would be done without resorting to brute force computer techniques.
I'm guessing the puzzles start with the solution, then remove squares until some desired degree of difficulty to reconstruct the solution is achieved. The Times puzzles are graded "easy" "moderate" and "diabolical".
1) Are all "solved puzzles" the same intrinsic complexity, or are some intrinsicly easier than others.
2) How do they validate that the solution for a puzzle is unique, and how do they grade the level of difficulty.
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