Erasable Games Weblog

(Sudoku in words and pictures)

Archive for March, 2007

Domino Sudoku

Friday, March 30th, 2007

Domino Sudoku

The original starting numbers for this puzzle are from Gordon Royle’s Sudoku Patterns (Strangely Familiar Family) Number 17. It is a 17 hint puzzle, but I added the 5 to represent all the digits using Sudoku Solver By Logic to verify where to place it.

Twin Sudoku

Sunday, March 25th, 2007

Twin Sudoku
Without instructions, I’m showing (by example) how to do these two interrelated and yet independent Sudoku puzzles. Thanks to Henry Kwok for the idea, although his example maps two sets of digits, which may be more difficult (confusing).

Word Search Sudoku

Sunday, March 18th, 2007

Word Search Sudoku

I’m always amused that I can’t always pronounce Sudoku properly all the time. I guess I need another year of practice. There is an upcoming book by Frank Longo called Word Search Sudoku (Mensa) to be published in April 2007.

More 2007 World Sudoku Championship And More Color Sudoku

Sunday, March 18th, 2007

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.

Sudoku Is Easy!

Sunday, March 11th, 2007

Sudoku Is Easy!

Depending on how tired I am, some of my sudoku efforts look like this. I’m sure this one can be solved, (Since I verified a single solution with Sudoku Susser Software). Perhaps I should have reduced the size of all the numbers even further?

2nd World Sudoku Championship

Sunday, March 11th, 2007

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.

Linear Sudoku

Sunday, March 4th, 2007

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.

Usenet And Sudoku Susser

Saturday, March 3rd, 2007

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.