Sudoku

a game by Sudoku

I have been playing this online Sudoku puzzle lately. I generally don't play the paper versions that come in the newspaper because they take too long. This online version has several features that make it attractive. It:

• has large numbers that are easy to read,
• will highlight all instances of a number when you click on one,
• provides a notation service so you can record possible values Even better it will completely erase a notation with a click, a real bonus in a house where all the erasers are dead or gone.

It would be even better if you could make notations using the keyboard, or make repetitive notes without having to select the same number over and over again. And highlight bars to show which rows and columns are currently occupied. And maybe an automatic solver so you could just watch it being solved. Hey! Wait a minute buddy!

It also has four levels of difficulty:

1. Easy, takes me between five and ten minutes and can be done using simple elimination techniques.
2. Medium, takes between 10 and 20 minutes. Requires more cunning and, depending on how sharp I am feeling, may require making notes.
3. Hard, take between 20 and 40 minutes. Almost always requires making notes.
4. Expert takes about an hour. I have not figured out to determine the solution for these. I can get part of the way there, but at some point I will have to make a guess. The puzzle will tell you if you guessed wrong, but it will add a penalty to your time. I haven't tried it, but you might be able to get a better time just by guessing than by trying to solve it.

I worked out all of the basic techniques myself, but evidently I am still missing some, so I went a-Googling, and I found that people have developed some more advanced techniques like Swordfish and X-Wing.

Update: You can use the keyboard to put numbers on the board. However, the keys on the numeric keypad don't work. Only the ones in the row about the regular alphabet keys will work. Bizarre side-effect of Firefox perhaps?