I first heard about sudoku yesterday and after the first try I developped a pen and paper algorithm which solves any solvable sudoku without needing higher brain functions.

first step:

subdivide each field of a 9x9 sudoku grid into 9 squares (3x3). each of these subfields is used to represent a digit from 1 to 9, choose a numbering convention for the subfields, like

123

456

789

a cross in a subfield signifies that the corresponding digit cannot appear in this field.

example:

xx_

x__

_x_

(this field can be 3,5,6,7 or 9, but not 1,2,4 or 8)

second step: translate the sudoku into the new form.

For each supplied digit, fill the subfields not corresponding to the digit.

for example, 5 becomes

xxx

x_x

xxx

Definition: zone of influence: each field has a zone of influence, in the traditional sudoku these are the associated row, column and block (variants could define other zones of influence)

repeat

- choose a field with a single empty subfield.

- draw a zero in this empty subfield (zero is used to remember that the influence of this field has been computed, once and for all).

- in this field's zone of influence, add a cross in the same subfield of all other fields.

until the puzzle is solved.

(that works if you make no mistake, and the initial conditions determine a single solution)

the solved grid ooks like this

xx0 xxx x0x xxx

xxx x0x xxx xx0

xxx xxx xxx xxx etc...

last, translate the solution to numbers again

3 5 2 6 etc...

kind regards,

Dominik Schlaefli