Grid and bear it

Huw Thomas explains how to get pupils at your school hooked on Su Doku, the craze that has gripped the nation

The menace of Su Doku grows. What began, in the UK, as a puzzle in The Times, has now spread to several other newspapers. Not wanting the children at my school to miss out on the craze, I've devised a few ways to get pupils hooked.

The only way to learn what Su Doku is about is to do one. Take a look at the example in Figure 1, a table of nine rows by nine columns totalling 81 little squares, known as cells.

The big square is divided into nine smaller mini-grids of nine squares. The challenge is to enter missing numbers, such that each row, each column and each mini-grid contains the numbers one to nine. It can all be done in logical steps - guessing doesn't work.

Tips

* Look at the rows of mini-grids. In the top of this example, the middle and right-hand mini-grids each contain a seven. That means there is only one place the seven can go in the left-hand one - to the left of the six.

* Look at squares and work through each number, asking "Could it go here?"

Sometimes there is only one option. Take the mini-grid at the centre of this Su Doku. There's only one number that can go above the two and three.

It can't be nine - there's already one in that mini-grid, it can't be eight - there's already one in that row, it can't be seven, and so on.

* Once you answer that one, you can then try the cell in the bottom right of that mini-grid, under the six and nine. Ask yourself: what's missing? Take the second column from the left. It's got six, five, seven, nine and four. The one, two, three and eight are missing. Only one of those numbers can go between the nine and the four. And if you've followed the second tip two above, there's only one number that can go in the fourth cell down. The other two figures now have a logical place in the column.

Easing in

There are a few ways of exploring how a Su Doku works with children, before embarking on an actual puzzle.

Incomplete grids

Figure 2 shows a grid, three by three. Can they put in the numbers one, two, three so that every row and column contains each number?

Blank grids

Using the blank grid in Figure 3, ask the children if they can enter the numbers one to four, so that each row, column and mini-grid contains each number only once. If they can do this, can they also create a nine-by-nine version?

Mini Su Doku

The Su Dokus in Figure 4 have a four-by-four grid and are made up of mini-grids consisting of four squares. The challenge here is to enter the numbers one, two, three and four so that each row, column and mini-grid contains each of those numbers only once.

These puzzles take us into two areas of the curriculum - it involves us in reasoning about puzzles and it's a great way for children to work on their capacity to explain their thinking.

Main thing, though, is they're addictive fun.

* Wayne Gould's collection The Times Su Doku Books 1 and 2 (pound;5.99 each) are published by Times Books.

Electronic puzzles can be found at www.sudoku.com

Huw Thomas is headteacher of St John's Church of England School, Sheffield

THE SU DOKU STORY

The term Su Doku roughly translates "Number Place" and the craze in this country was started by Wayne Gould, a puzzle enthusiast, who first encountered Su Doku in a Tokyo bookshop and brought the idea back to the UK. He now produces the daily puzzle for The Times, and it has spawned an array of imitators in other newspapers.

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