Last weekend, I spent waaaay too much time on the DC Examiner's Classic Sudoku puzzle (6 star difficulty). But that was a week ago, and I've been doing a lot of puzzles. I can't be sure, but I think the programming project might also be causing me to have some improvement as well.
I blew through the 5 star Sudoku Pacific rather easily. Then, I turned my attention to the Sudoku Classic puzzle. At about 30 minutes in, I was pretty sure it was another diabolical puzzle. I inked in the numbers I was certain about, and switched to a pencil. I had to choose between a 6 and an 8 at Row 4, Column 5-- wound up choosing the 6 and discovered about 6 minutes later that path resulted in a conflict. At that point, I had to erase everything from the past six minutes worth of work. That was disheartening. I chose the "8 path" at that point, and was rolling along until an hour and 18 minutes had passed-- and that's when I hit a brick wall.
I've never heard of such a thing as a "double diabolical" puzzle, but I found myself once again in the position of being unable to eliminate any of the remaining possibilities on the grid and having to pick one of two pairs. I suppose it is possible that I overlooked something, but in every row and column the number of empty squares and the number of possible values were equal. At this point, I was so mentally exhausted, I stopped for lunch and took a break to watch an episode of "My Name Is Earl" on the DVR.
Then, I came back and took a new stab at the puzzle. Once again, I couldn't find any way to break the chain of possible values down further-- so I inked in the numbers I'd picked once again (no turning back now, right!?) and choose a path to explore. Fortunately, it turned out to be the correct one. Total time spent on the puzzle: 1 hour and 48 minutes.
Now, I need to get some aspirin and lie down. ;)