What is the minimum number of filled cells in a sudoku puzzle for it to have a unique solution?

Answer 1

The answer to your question is unsolved, but no known Soduku puzzle has less than 17 givens. No one has managed to construct a proof that 17 is the minimum.

Answer 2

Whenever you have a sudoku SOLUTION you can use a sudoku generator to the hide cells whilst maintain the uniqueness of the solution. This number is different for each puzzle.

This answer to this question becomes even more complex when you consider some of the sudoku variants like the sudoku-ball (see also http://www.flickr.com/sudokuball or http://www.sudoku-ball.com) which contains well over 1000 cells (I didn't count the exact number but it is huge).

Probably the question should have been phrased like: "What is the maximum number of hidden cells by which it is possible to create a sudoku with a unique solution".

I am not sure what the exact answer to this question is but remember reading that someone had created a sudoku puzzle which only had 16 initial numbers displayed. I will try to locate the source of that information and post it here if I can retrieve it.

Answer 3

This website states

"Gordon Royle of the University of Western Australia has collected more than 24,000 examples of uniquely solvable grids with 17 givens, and he has found none with fewer than 17, but a proof is lacking."

So, nobody has proved it, but it appears that 17 is the minimum number of filled cells necessary to ensure there is only one unique solution.

Answer 4

Zero filled cells. All sudoku puzzles have unique solutions. The number of filled cells has nothing to do with uniqueness of solutions. The number of filled cells only affects the difficulty of finding the solution.

Answer 5

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