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How few filled cells could appear on a valid Su Doku puzzle?

April 26, 2017appear cells filled puzzle su doku valid

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How few filled cells could appear on a valid Su Doku puzzle?

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I aim to produce a definitive answer to this question shortly – the answers are at most 8 for 3×2 Su Doku, 19 for 3×3 Su Doku and 42 for 3×4 Su Doku. (See the Su Doku Brain of Britain page for examples of such puzzles.) I haven’t constructed a mathematical proof in order to demonstrate these values – it’s just that, as yet, I haven’t been able to build puzzles with fewer initially-filled cells.