Category: Sudoku Variants

I discovered this distant cousin of Sudoku in the newsgroup rec.puzzles a couple of weeks ago. Kevin Stone has provided an enhanced user interface with notes for doing daily Hitori puzzles on his website brainbashers.com. His site provides 3 sizes: 5×5, 7×7 and 9×9. These puzzles change daily. Previous Puzzles revert to Neil Berget’s beta website hitoriconquest.com. An archive is not yet available. Hitoriconquest.com offers 5×5, 8×8 and 12×12 size puzzles, as well as a tutorial on how to play.

Hitori is Japanese for “Let Me Alone”. More information is in the Wikipedia Article. The Nicoli Company Website has an animated (flash) tutorial.

The rules are straightforward. Shaded cells cannot be contiguous. They are either separated by a non-shaded (‘white’) cell or touch at their corners. Non-shaded cells, on the other hand, must be contiguous (e.g. at least one side must touch another ‘white’ cell’s side.) The result is that when a puzzle is solved, one can travel a connected path of ‘white’ cells. Puzzles provided by these web sites lead logically to unique solutions.

Hitori exercises your brain differently than in Sudoku. It’s almost as if your luggage is too full to close and you must toss expendable articles so that it fits. I found it necessary to go down each row, making the numbers unique, then going across each column. When this is done, I checked that I didn’t isolate any ‘white’ cells. That seemed to be sufficient to form a correct answer.

Both websites have a (partial) solution checker and it can show any mistakes that are evident as well as if it is all correct. I definitely enjoy this variation on a Sudoku board.

Since you can play Chess by mail (See FAQ) or use a Chess Correspondence Server, I wondered how it would be possible to solve Sudoku by mail. In this case, it requires $4.50 for the 9 denominations of 1 cent through 9 cent stamps. Do not use rare stamps. You won’t be thanked. For those of you that like to solve Sudoku puzzles quickly, I believe that this variant will slow you down. The puzzle is considered neither easy nor hard.

While there are sites that claim the ability to do Sudoku by mail, this simply means that the site is willing to send you email (daily) with one or more Sudoku puzzles for you to solve on your own computer. This is convenient, but no way will a puzzle take days, weeks or months, iteratively, to complete.

This variant is a consequence of another hobby I used to do involving Astrology. The planetary symbols are called glyphs which I dutifully memorized and matched to the planets and (and asteroids) in our solar system. They are listed above for your convenience. I used the Hamburg Symbols (True Type) Font to produce the glyphs.

Although it is arguable as to whether Pluto can be considered a major planet, I have no wish to diminish its importance to astrological interpretation. Scientists seem to have a consistent track record of saying one thing and subsequently changing or contradicting their original statement. There’s always a reason. I’m just waiting for the next reason (in 2015) to reinstate the planet.

As usual in these kinds of Sudoku variations, each symbol represents one of the non-zero units digits. You can first transcribe it to numbers or further flex your mind and solve it as is.

This variant comes from the 2nd Annual World Sudoku Championship instruction booklet (pdf). This competition was held In Prague earlier this year. The idea is to consider the sudoku puzzle also as heights of buildings as seen from the top down. The total counts on each edge (side) represent how many buildings are viewable from that location. Note that taller buildings (higher numbers) hide shorter buildings (lower numbers). Once again the starting numbers are sparse due to the edge clues.

Sudoku X has been an alternative to regular Sudoku puzzles, when I wanted some minimal relief. Having a vest pocket pair of constraints when I was otherwise reduced to guessing was nice. The site: easton.me.uk provides a downloadable (Windows) Puzzle Generator for Sudoku X (Nothing on this variant, though).

Because this variation is not one that Sudoku Solvers solve programmatically, I had to reverse engineer the solution by specifying a proper set of values for the Y and then solving by adding one number at a time and insuring that the result did not produce a conflict with the other cells. I stopped when there was a single unique solution. (I used the Web Based: Sudoku Solver By Logic.) I’m not sure if I could have provided fewer clues, but feel free to erase as many as you want and see if you can solve it that way.