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Q&A: How difficulty level of Sudoku puzzles is determined

Determining Sudoku difficulty

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I would like to know how the difficulty level of the Sudoku puzzles in BayLink is determined. I ask because sometimes I have a great deal of difficulty with a "medium" and at other times a "hard" is straightforward and just pleasantly challenging.

Merl Reagle supplies the Sudoku for the BayLink section of the St. Petersburg Times, so we asked him how he determines the difficulty level. He writes:

"We create our Sudokus using a variety of software and grade them using a variety of systems. When I solve them myself I find that the easy ones are always easy, but that out of every 10 mediums, two strike me as more on the hard side, and out of every 10 hards, two strike me as more on the medium side.

"There are a couple of reasons for this. For example, I might start solving a hard Sudoku in a way that happens to be the perfect strategy for that particular puzzle, and thus it will seem more like a medium. Or I may be solving a medium and I keep missing the only breakthrough point that would allow me to advance, and thus that puzzle will seem like a hard — but since the Sudoku is still a medium after I get past that one roadblock, it's graded as a medium overall.

"I have five or six strategies that I use when solving, all of which involve what I call 'quick look' logic (not the complicated extrapolating kind that the superhard Sudokus often require), and sometimes I use one of my advanced strategies early on — often without realizing it — and an otherwise hard Sudoku seems to fall much faster than usual.

"So it's a combination of how the software judges hardness and how each solver solves."

Why no All-Star Game here?

During the Major League Baseball All-Star Game, one announcer said there are only two MLB teams that haven't hosted the All-Star Game. Tampa Bay is one of them; who's the other?

The Florida Marlins and the Tampa Bay Rays are the only teams that have yet to host an All-Star Game, since the event was held in Arizona in July. There are probably two reasons for this:

• Relative newness. The Florida Marlins began playing in 1993, and the Rays began in 1998. They are two of the four most recent teams to be awarded franchises, the others being Arizona (1998) and Colorado (1993).

• Stadiums. Major League Baseball has very low opinions of the stadiums the Rays and Marlins play in.

The Marlins won't have that problem for long. Their new stadium is going up now and is expected to be ready for opening day 2012. And because of that, the Marlins are said to be in the running for the 2015 game.

The Rays have no new stadium plan in place, though it is a topic of conversation, and therefore are not expected to be considered for an All-Star Game.

To play: Fill in the grid so that every row, every column and every 3-by-3 framed box contains the numbers 1 through 9 exactly once. The solution is unique.

Yesterday's answer

Q&A: How difficulty level of Sudoku puzzles is determined 08/01/11 [Last modified: Monday, August 1, 2011 11:40pm]
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