Good grief!
Just wasted about twenty minutes on a Sudoku puzzle (from a cheap book I usually keep in the loo). My usual time for the puzzles in this book - which are all fairly easy, despite being marked "beginner, intermediate" and "expert" - is about four minutes. This one just wouldn't come out... until I realised that there were actually two possible solutions, neither of which was erroneous. Basically there were two pairs of 2 and 4, on the left side and in the middle - you could have 2 on top and 4 below to the left, with 4 on top and 2 below in the middle, or vice versa, without affecting anything else.
To say that I'm annoyed is putting it mildly - these things are supposed to have ONE unique solution. But someone messed up the error checking and this is the result. The real bummer is that I can't now trust the rest of the puzzles to be OK, so I might as well bin the book.
Later: Found another one, this time with four pairs (on horizontal lines 4 and 5) which give a valid solution either way if they're all flipped vertically. I'm now finding looking for the errors more interesting than doing the puzzles!
To say that I'm annoyed is putting it mildly - these things are supposed to have ONE unique solution. But someone messed up the error checking and this is the result. The real bummer is that I can't now trust the rest of the puzzles to be OK, so I might as well bin the book.
Later: Found another one, this time with four pairs (on horizontal lines 4 and 5) which give a valid solution either way if they're all flipped vertically. I'm now finding looking for the errors more interesting than doing the puzzles!