Sudoku

A friend of mine introduced me to a game called Sudoku, a kind of puzzle which first became popular in Japan and is now quite popular in Britain. Sudoku puzzles are published along with crosswords in several British newspapers (e.g. Guardian, Times).

This is one of those misleadingly simple games which in fact can be fiendishly difficult. Your goal is to fill in the blank spaces on a board like this:




There are just three rules:

1. Each column must contain the digits 1 2 3 4 5 6 7 8 9.
2. Each row must contain the digits 1 2 3 4 5 6 7 8 9.
3. Each 3x3 block must contain the digits 1 2 3 4 5 6 7 8 9.

If you begin by considering a 3x3 block, and asking yourself "Where could I put the 4? Where could I put the 6?" and so on, you eventually find numbers which can only go in a particular square. For instance, in the lowest right-hand block in the above example, the "1" can only go left of the 7; in any other square, you'd end up with two 1's in a single row or column.

As you fill in a few more numbers, you can look at rows or columns to see which numbers are still missing and where you might place them. It's easy to learn the basic idea, but a lot of logic enters into it. It's great exercise for the brain, let's put it that way!

This site has three games per day you can solve on-screen (or print out, I assume): one easy, one medium, and one hard. Check it out....