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More 2007 World Sudoku Championship And More Color Sudoku

I’m slowing catching up on the news: On February 3, 2007, The World Puzzle Championship announced the U.S. Sudoku Team Members for the 2007 World Sudoku Championship.
They are:

  • Nick Baxter, Captain and Members:
  • Grayson Holmes (placed 50th in 1st World Sudoku Championship March 2006),
  • Wei-Hwa Huang (placed 2nd),
  • Jonathan Rivet,
  • Jim Schneider (placed 28th),
  • Thomas Snyder (placed 1st),
  • Jason Zuffranieri

In the livejournal community called worldpuzzle, there are many details about the upcoming World Championship including instructions (a downloadable pdf file).

There are new kinds of puzzles depicted, which are different from those in 2006. I especially like the puzzle called Paint It Black, which is a blend of a Sudoku Puzzle and a Paint By Numbers Puzzle.

Two Color Sudoku Sites that I noticed are a Color Sudoku Journal Article and a Color Sudoku Solver in MS Excel.

The Journal of Chemical Education is publishing an article called “Chemistry of Art and Color Sudoku Puzzles” by Michael J. Welsh of the Department of Science and Mathematics, Columbia College Chicago, Chicago, IL 60605

The abstract describes what may be a fascinating connection between chemistry and color. Unfortunately a paid subscription to the Journal ($45 for US Individual) is required for both the full text of the article and the 3 puzzles and solutions file shown in the article.

Quite free is the Color Sudoku Solver via Excel Spreadsheet by Erkki Hartikainen: downloadable xls file. This spreadsheet solver permits you to map the digits and colors in either direction.

One particularly handy feature is the ability to modify colors depending on your own eyes’ ability to distinguish contrasting colors. The color solver is based on a number Sudoku solver by David Ireland.

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2nd World Sudoku Championship

This year, From March 28 Through April 1, 2007, The 2007 World Sudoku Championship will take place in Prague, Czech Republic. This championship is sponsored by the World Puzzle Federation. The World Sudoku Championship competitions consist of individual as well as National Team competitions.

It seems like it would be an interesting way to play along (nearly concurrently) if the puzzles are published on that site during the competition. I’m looking forward to it. I missed the 1st World Sudoku Championship and conference held last March 2006. Twenty-two National Teams were represented there.

By downloading the 2.4 MB pdf file via the Sudoku booklet link, you can see the kinds of Sudoku variants that the contestants were exposed to and can solve separately and check your answers with the solution. The game titles are given in the Schedule page, consistent with the instruction booklet.

It’s an amazing collection of variants. Practicing for speed and correctness must be grueling as much before the matches as during competition play.

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Linear Sudoku

Linear Sudoku: Tickertape Or Mobius Strip?

The idea for using a string of 81 single digits [the solution] or 81 characters including the blank character [the unsolved puzzle] probably originated on Usenet due to the text based messaging used there. I’ve always been fascinated with Mobius Strips and Klein Bottles (the 3-D analogue). A very enjoyable, math oriented book first published in 1958, Edited by Clifton Fadiman, called Fantasia Mathematica conjectures about the possibilities raised by these strange objects, among other science fiction topics.

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Usenet And Sudoku Susser

Before the Web was in evidence in 1991 (see history), there was Usenet News, which started in 1979. It grew to consist of myriad newsgroups, even in the 1980s. Computer servers, as a public service, dedicated some of their storage to a rolling database of hundreds and later thousands of newsgroups containing messages going back several days to several weeks before the oldest messages were sloughed off in favor of the latest messages. The mechanism used was a form of uucp (Unix to Unix Copy) which stored and forwarded the message base from one Computer system to another.

Within Usenet, there existed binary newsgroups that allowed freeware, shareware, updates to existing applications that were regularly made available. See a short history of Usenet.

A while back, I was reading the newsgroup: rec.puzzles, a very large online discussion group, I searched for the subset of articles that involved Sudoku (using the Unison Newsreader on Mac OSX 10.3.9). From these (over a thousand messages), There was a message relating to the Multi-Operating System product (Freeware) called Sudoku Susser by Robert Woodhead.

He is the author of Two Sudoku books: Sudoku To Go! and Brainiac’s Sudoku Puzzle Book. The first is an adult puzzle book and the second one is more for kids or novice learners.

I’m impressed with Sudoku Susser. It is interesting because of its user interface support for various intermediate and advanced solving techniques. You can also drag and drop puzzles to solve from the Web or as files and the software will attempt to read it in.

Since the author of the books is the author of the software, Supplying the ISBN number to either book will automatically load all the puzzles in that book! The type of freeware requested is called tipware. I.e., pay what you can, if you want. I like this software’s user interface even better than that of the Seattle Times Sudoku Puzzle (which they offer via, which is my favorite online web interface.

I solved the initial easy puzzle to test how the default interface worked. Every move you make is tracked. All possibilities (variable sized depending on how many) are specified in the non-starting number squares, making the puzzle a fast pleasure to solve. When highlighting a square, the non-possibilities are also shown to verify your candidate value. There are options for toggling “annoying” sound effects and an “embarrassing” timer.

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Flickr Sudoku

A visually interesting mashup of Sudoku and Flickr involving pictures of numbers is shown in Flickr Sudoku. This is an online playable game, (although rendering for the Safari 1.3.2 browser is flawed at the bottom).

Unfortunately, the presentation reminds me of a numerical ransom note. This is not to minimize the great work that went into creating this site. I also like the various (random) Sudoku keyword searches on Google shown at the top. There’s a Time of Day Site called Human Clock that has found and created objects/photos with the correct hour and minute that uses a similar idea.

A more abstract version of the same concept is shown on Becky’s Web where 9 thematically grouped pictures and a blank picture are shown in a playable grid. Like the large varieties of layouts in Mah Jong Solitaire Software Puzzles, the original chinese characters are transformed into various alternative symbol sets.

I believe it is a good idea, when exercising the brain, to expose it to a variety of “settings” or contexts in which puzzle solving logic can be applied. The brain embraces the novelty and adapts to a more flexible solving environment.

Thanks to Webmaster for letting me know about these sites.

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Sudoku Coloring Puzzle

Ivars Peterson, written about last week here, has announced his departure from Science News and Math Trek Blog for a position as Director of Publications for Journals and Communications at the Mathematical Association of America (MAA). His new blog, due in March 2007, will be called: The Mathematical Tourist.

Within the MAA Online website, Ed Pegg, back in September 2005, surveyed the varieties of Sudoku and showed many actual variants, some of which are regularly published (especially in Japan). It is an excellent article and a testament to Sudoku puzzlers’ low tolerance for boredom.

I especially like the Cubic Sudoku, which contains 2×4 rectangles on the cube faces with 1×8 “bent in the middle” strips that comprise the “rows” and “columns”. I’m an easy mark for 3-D puzzles.

On a Dutch Web site called Sudokube that I roughly translated with the help of babelfish, there is a hybrid of Sudoku and Rubik’s Cube available for sale for only 7.49 Euros per. (It offers a reduction in price to 5 Euros on its home page.)

This is what I find ironic: the original Rubik’s Cube consisted of 6 colors that get ultimately arranged to have one color per face of the cube. Sudokube has produced a rubik’s-like cube with the digits 1 through 9, in order, on each face, when solved.

Whereas, in my Sudoku Coloring Boards Cartoon of February 10, 2007, I rendered a Sudoku puzzle into a color mapping and a pattern mapping of the digits 1 through 9 from the original starting numbers. I’ve not seen any instances of this variant anywhere else.

I believe this will be very attractive to people whose visual color sense is advanced and whose number sense has been stifled in early life or atrophied. Since I teach math and feel rather un-visual, does anyone else concur (or not) with this?

How do you go about solving the Sudoku Coloring Puzzle as shown in the Cartoon? It seems to me that using small colored dots to make temporary notes in the boxes is analogous to the small numbers one writes as permissible entries. Do you solve the puzzle quicker or slower than one with numbers?

Obviously, solving this is perfect for the Power SudokuĀ² white board and colored markers found elsewhere on If you lack 9 different solid color markers, you can assign patterns for the missing solid colors instead, although that makes small notes harder to write.

The Puzzle is reproduced here and downloadable as a pdf file:

Sudoku Coloring Puzzle 1 450px