So anyway, this morning’s Guardian sudoku has 20 numbers filled in out of the potential 49. That seemed low – 24 or so is more common, I think.
But it wasn’t impossible, and I didn’t have to resort to guessing at any point to finish it. Which brings me back to the question I ask myself from time to time, but can’t think of a way to figure out a priori: what is the smallest number of numbers that one needs filled in on a sudoku grid to make it solvable without guessing?
thelondonpaper’s “difficult” sudoku frequently beats me where the Gdn one rarely does, so clearly there are levels of difficulty even with roughly the same number of already-given squares. But how low can you go?