Su Doku is a mathematical puzzle syndicated in some newspapers, notably The Times. Despite it being called a mathematical puzzle there is no mathematics actually involved, solving the puzzles requires just simple logic. Su Doku was created by Wayne Gould.

A 9 by 9 grid is presented with most squares empty and a few having a single digit. The puzzle is to complete the grid such that each column, each row and each of nine non-overlapping 3 by 3 sub-squares has each digit 1 through 9 exactly once.

For example:

. . .  . . 7  3 . .
4 8 7  . . 5  . 2 .
. . .  6 9 .  . . .

. . 4  3 . .  6 . .
. 9 .  . . .  . 1 .
. . 8  . . 6  5 . .

. . .  . 6 9  . . .
. 1 .  5 . .  4 6 3
. . 5  2 . .  . . .

is solved as

9 6 1  8 2 7  3 4 5
4 8 7  1 3 5  9 2 6
5 3 2  6 9 4  1 7 8

7 5 4  3 8 1  6 9 2
3 9 6  7 5 2  8 1 4
1 2 8  9 4 6  5 3 7

8 7 3  4 6 9  2 5 1
2 1 9  5 7 8  4 6 3
6 4 5  2 1 3  7 8 9

Note that it is possible to set starting grids with more than one solution and to set grids with no solution.

External links

• http://www.sudoku.com