## Notice

I am no longer posting new puzzles to this blog. For all of my Sudoku puzzles, old and new, please visit Sudoku in another section of this website. I will still create and offer new puzzles, in batches of a couple of hundred, once a week or so.

## Sudoku #20

Category: Sudoku
Tue, 12 Jul 2005, 09:22

Yesterday, I was surfing around some of the other Sudoku web sites, and I came across one that offered some puzzles described as "devious". Well, of course, I had to try them out. The first puzzle turned out to have no solution. It simply had an invalid starting arrangement. The second was easy to solve, needing just the basic solving methods. The third was a bit more interesting.

When I fed the third "devious" puzzle to my solving program, it had to resort to a trial and error, backtracking method to find a solution. Backtracking means either one of two things. First, it could mean that my program doesn't know about some particular analytical solving technique. Second, it could mean that the puzzle has multiple solutions. A bit more analysis revealed multiple solutions for the puzzle.

Are multiple solutions acceptable in a proper Sudoku puzzle? I would argue that they're not. Every puzzle should have one distinct solution discoverable through a series of analytical steps. Otherwise, you can drive yourself crazy trying all sorts of analytical approaches.

As for the puzzles I post here, as far as I know, they are all solvable analytically. Some of the steps may be tricky, but you shouldn't have to resort to trial and error to solve any of them. If you don't think that's true about any of these puzzles, send me an e-mail.

Hans

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