Sudoku Galore

Sudoku Galore

Anyone who has read my blog since late October knows that I am somewhat of a Sudoku fanatic. Apparently I'm not the only one, as sudoku games appear in more than 100 newspapers worldwide. Now, perhaps because I have posted so many sudokus and monster 16 x 16 sudokus on my blog, I find that many other people are sending me links to their sudoku games. These games come in three varieties.

First, there is the sudoku game which you can download to your computer and play while offline; check out Mark Klocek's (free) Pure Sudoku, or if you are willing to spend some money on a similar program you can get one from Sudoku.com.

Next, there are the sudoku games that you can add to your blog or website. Vulkanino showed me Logicando.net's version in a comment back in February. The version I publish on this blog is available at SudokuPuzz.com. I found Free Sudoku via Grilles de Sudoku; besides the regular sudokus (with 3x3 regions arranged in a 3x3 grid, for a total of a 9x9 grid), this one also has versions with 3x2 and 3x4 regions.

Finally, there are the type that you can play online; these include the ones listed in the paragraph above, but the following are not available to add to your own blog or website. Check out Sudoku Hints (which also allows you to input a sudoku from another source) and Websudoku. For a twist, try Sopranos Sudoku, which uses pictures of characters from the hit HBO series rather than numbers. And finally, Steven Van Vaerenbergh's Squobble adds an extra dimension to regular sudoku, as all the numbers have colours, each of which appears only once in every row, column and 3x3 region.

One more site I should mention: if you want to create your own sudokus (or if you're just a cheatypants and want to solve them without any effort), then check out SourceForge's Sudoku Solver.

Now, it turns out that rather than being merely a pleasant diversion, there is actually a practical application to sudoku - or more accurately, there is a practical application that turns out to also solve sudoku:

Cornell physicist Veit Elser has been engrossed recently in resolving a pivotal question in biological imaging. So he hasn't had much time for brainteasers and number games.

But in discovering an algorithm critical for X-ray diffraction microscopy, Elser and colleagues solved two problems. First, they gave researchers a new tool for imaging the tiniest and most delicate of biological specimens. And second, they discovered that the same algorithm also solves the internationally popular numbers puzzle Sudoku.

Not just one puzzle. All of them.

...The so-called difference-map algorithm, which Elser says could have applications from productivity optimization to nanofabrication, tackles problems for which the solution must meet two independent constraints. In the case of Sudoku, the constraints are simple: Each of nine numbers, considered alone, appears nine times in the grid so that there is only one per row and column. And all nine numbers appear within each of the nine blocks.

In X-ray diffraction microscopy, the constraints are more complex. But the beauty of the algorithm, as Elser demonstrates, is that complexity doesn't matter. By applying the algorithm to the jumble of raw data from such an experiment, researchers can now reconstruct from it a clear, detailed image.

The page with the X-ray diffraction microscopy also includes a ginormous 25x25 sudoku; I downloaded the image of that, cleaned it up, and posted it above right. Click on the image for a larger version, and enjoy. (Kiraly, I told you I was going to put a 25x25 behemoth up here one day!)

Update: When I copied the huge sudoku from the Science Daily column, some of the letters in the puzzle weren't very clear, and I made a mistake; the 17th row had two M's and no H's. That problem is fixed now.

Update 2: Hold yer horses! After Kiraly pointed out one error that I had made in my transcription, I decided to see if there were more; sure enough, there were. I had missed one letter altogether, and had a couple more incorrect: in the original image it is very difficult to tell the difference between the letters H, M, and N. The corrected version (for sure this time) of the ginormous sudoku is now posted above, but even now I am not certain whether the letter in the first row and tenth column is an H or an M.

HOWEVER: It doesn't matter what letter goes in that disputed spot. Either way, according to SourceForge's Sudoku Solver there is no solution to this sudoku, contrary to the assertion in the Science Daily article that the solution will spell out the name of one of Cornell University's founders.

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