## October 17, 2005

### Sudoku

On the flight home from Chicago I noticed that the United in-flight magazine was proudly proclaiming itself the first airline magazine to offer a Sudoku puzzle. Sudoku is a logic puzzle where you have to fill out (as an example) a 9x9 grid with numbers such that each row, column, and 3x3 subgrid have the numbers 1 through 9 appearing once. For each puzzle the grid is presented with some of the numbers filled in and then you have to deduce where the other numbers go. For example if eight of the spots in a row are filled in and the only number missing is 8, you know that 8 goes in the remaining empty box.

I worked through the four examples in the magazine...the instructions estimated 10 to 30 minutes each but they took longer, as I figured out how to solve these things. You can solve them just by looking at a column and saying "OK the 4, 5, 7, and 9 are missing and the 4 can't go in this row or this box so it goes here..." but you quickly adopt some shortcuts such as noticing that a 4 appears in two out of three 3x3 boxes in a row, which means there must be a 4 in the third box but not in the row that the other two were in, which narrows it down to 3 spots...etc, etc (it's hard to explain exactly what I mean but you'll see if you start solving them).

These are evidently the latest craze in puzzles. Personally I'll stick to the cryptic crossword in the Atlantic but they are an interesting diversion (as it happens sudoku just got first-posted in this Slashdot roundup of math/logic riddles). One nice thing is you can make them basically any size. For example here, from a website that has them in various sizes, are some 4x4 ones (so each row, column, and 2x2 box has to have the numbers 1 through 4 in it).

Posted by AdamBa at October 17, 2005 06:36 PM

http://proudlyserving.com/cgi-bin/mt-tb.cgi/344

Hope you don't mind me posting an URL. If so, feel free to delete this comment.

Mark Huckvale has published a bunch of su doku puzzle books and even has an online puzzle generator with instructions here:

Posted by: Drew at October 17, 2005 10:01 PM

See the excellent WikiPedia article on Sudoku:

http://en.wikipedia.org/wiki/Sudoku

Lot of tips on solving as well as a discussion of the mathematical properties of the game.

WebSudoku:

http://www.websudoku.com/

is an excellent (FREE) online version of the game. I'm still in the 5-7 minute solving time for the Easy Sudoku on this site (but I have a friend who's doing under 3-minute solves!)

- Mike

Posted by: mckoss at October 19, 2005 06:59 AM

Cool. I just noticed the new TV Guide has a "Wordoku" (with letters not numbers). It's actually pretty hard. The letters are from the name of a TV show (e.g. it might be N-U-M-B-E-R-S plus 2 more) and they embed the name of the show somewhere. So far (2 of 2) I have not been able to solve it without leveraging this fact (i.e. looking for the only place where the word "NUMBERS" appear in order in the puzzle and then filling it in). I'm not sure if this is by design or I'm just lame. Actually I'm curious how you design a sudoku so it unfolds just right.