I was just pottering around the web and was reading some articles about how many numbers you have to have in a sudoku puzzle in order to be able to solve it uniquely.
It turns out that the lowest number is 17, or at least no-one has actually found any puzzles where 16 givens lead to a solution. I'm not entirely certain if there is a proof that you need at least 17 as it seems to vary depending on which site you go to whether there is a valid proof out there or whether it is simply that no-one has ever found one despite all those computers running trying to make one and therefore almost certain that there isn't one out there!
I was looking in some newspapers and books I have here, and I've never seen a puzzle published in a magazine or newspaper with less than 20 givens as far as I am aware... which makes you think that they must be pretty rare.
What's the least number of givens you've ever seen in a sudoku puzzle?
I'm thinking that it might be because the puzzles in newspapers have symmetrical givens... I wonder what the least number you need in order to solve a sudoku puzzle with symmetrical givens is?!
How to solve a Sandwich Sudoku If you know the rules of sandwich sudoku but aren't sure how best to tackle a puzzle, this video walks through a puzzle and how to solve it to get you started. Highly recommended, as it's a really fun puzzle type to solve...
If you've never solved a sandwich sudoku, then a 6x6 puzzle is a good place to start. You can have a go at solving the puzzle featured in the video here: 6x6 Sandwich Sudoku Puzzle Online
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