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Tuesday, July 11, 2006
Need Help With Sudoku -vwv

I spent most of Sunday sitting at the hospitality desk for the 37th International Physics Olympiad at the Meritus Mandarin. Since most of the international delegates are not at the hotel most of the time, I had a lot of time to spare, so I tried to solve two Sudoku problems.

1. What is the minimum number of blanks a Sudoku puzzle can have and still have more than one unique solution?
2. What is the maximum number of blanks a Sudoku puzzle can have and still have only one unique solution?

Actually, I contemplated problem 2 a long time ago but never really found the answer. And I still could not find the answer after thinking about it for half of Sunday. So I tried to solve the inverse problem, which is problem 1.

Problem 1 was quite easy. It took only a few minutes. The answer is 4 and the proof is not too difficult either.

Out of curiosity, I checked Wikipedia and according to it, problem 2 is unsolved. That sucks. So anyone out there who can solve it please tell me the answer yah, I would really like to know.

-- permalink --
Yiheng made
9:50 PM


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