On Mar 26, 2015 6:31 AM, "Marko Rauhamaa" <ma...@pacujo.net> wrote: > > "Frank Millman" <fr...@chagford.com>: > > > Here is another python-based sudoku solver - > > > > http://www.ics.uci.edu/~eppstein/PADS/Sudoku.py > > > >>From its docstring - > > > > "A proper Sudoku puzzle must have a unique solution, and it should be > > possible to reach that solution by a sequence of logical deductions > > without trial and error. > > I don't think that statement holds water. Trial-and-error is at the > basis of deduction (reductio ad absurdum). The human solver employs it > in their head. The question is, what is the difference between > pen-and-paper and in-your-head for a computer program?
It's an accurate characterization of the sort of puzzles that are typically presented as sudoku. I don't think that I have used trial and error, in my head or otherwise, in any sudoku I have ever solved. > > It solved Marko's original puzzle and Ian's puzzle in less than a > > second. It could not solve Marko's second one, returning "impossible" > > immediately. Perhaps this is why that puzzle was described as being so difficult: it required steps that human solvers don't usually take.
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