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What is sudoku?

You would imagine that with such a name this puzzle originated in Japan, but it has been around for many years in the UK. However, the Japanese found an example under the title ‘Number Place’ in an American magazine and translated it as something quite different: su meaning number; doku which translates as single or bachelor. It immediately caught on in Japan,where number puzzles are much more prevalent than word puzzles. Crosswords don’t work well in the Japanese language. The sudoku puzzle reached craze status in Japan in 2004 and the craze spread to the UK through the puzzle pages of national newspapers. The Daily Telegraph uses the name Sudoku, but you may see it called su doku elsewhere. However, there is no doubt that the word has been adopted intomodern parlance, much like ‘crossword’. Sudoku is not a mathematical or arithmetical puzzle. It works just as well if the numbers are substituted with letters or some other symbols, but numbers work best.

by Michael Mepham

About guessing

Try not to. Until you have progressed to the tough and diabolical puzzles, guessing is not only totally unnecessary, but will lead you up paths that can makethe puzzle virtually unsolvable. Simple logic is all that is required for gentle and moderate puzzles.

3 7 9 4 4 6 5

8 3 4 4 8 2 1 1 7 1

© Crosswords Ltd, 2005

Making a start 1

Logic will go a long way to solving most sudokus. Ask yourself questions like: ‘if a 1 is in this box, will it go in this column?’ or ‘if a 9 is already in this row, can a 9 go in this square?’ To make a start,look at each of the boxes and see which squares are empty, at the same time checking that square’s column and row for a missing number. In this example, look at box 9. There is no 8 in the box, but there is an 8 in column 7 and in column 8. The only place for an 8 is in column 9, and in this box the only square available is in row 9. So put an 8 in that square. You have solved your ﬁrst number.8 3

Here is an unsolved sudoku puzzle. It consists of a 9x9 grid that has been subdivided into 9 smaller grids of 3x3 squares. 9 4 1 8 3 Each puzzle has a logical and unique solution. To solve the puzzle, each row, column and box must contain each of the 4 6 5 7 1 numbers 1 to 9. 7 Throughout this document I refer to the whole puzzle as the grid, a 1 2 5 3 9 small 3x3 grid as a box and thecell that contains the number as 7 2 4 a square. Rows and columns are referred to with row number ﬁrst, followed by the column number: 4,5 is row 4, column 5; 2,8 is row 2, column 8. Boxes are numbered 1−9 in reading order, i.e. 123, 456, 789.

Copyright © 2005 Crosswords Ltd

#5096

© Crosswords Ltd, 2005

#5096

3 7

8 3 4 4 8 2 1

The challenge

1 2 5 3 7 2 4

7 9

8

3 7

83 4 4 8 2 1

8 8

2

Continuing to think about 8, there is no 8 in box 1, but you can see an 8 in rows 1 and 2. So, in box 1, an 8 can only go in row 3, but there are 2 squares available. Make a note of this by pencilling in a small 8 in both squares. Later, when we have found the position of the 8 in boxes 4 or 7 we will be able to disprove one of our 8s in box 1.

3 7

8 3 4 4 8 2 1

8 84

There is a similar situation with the 4s in boxes 4 and 5, but here the outcome is not so deﬁnite. Together with the 4 in column 7 these 4s eliminate all the available squares in box 6 apart from two. Pencil a small 4 in these two squares. Later on, one or other of your pencil marks will be proved or disproved.

9 4 4 6 5

1 7 1

8 3

9 4 4 6 5

1 7 1

8 3

4 4

© CrosswordsLtd, 2005

#5096

3 7

8 3 4 4 8 2 1

8 8

3

We were looking at box 9. As you can see, there is a 2 in boxes 7 and 8, but none in box 9. The 2s in row 8 and row 9 mean the only place for a 2 in box 9 appears to be in row 7, and as there is already a 2 in column 8, there is only one square left in that box for a 2 to go. You can enter the 2 for box 9 at 7,7.

3 7

8 3 4 4 8 2 1

8 8...