This page helps you solve sudoku puzzles by showing choices satisfying two simple rules: at-most-one and at-least-one of every digit must appear in every row, column and square.
Choices that violate the at-most-one rule are omitted. Alternatives to digits that must be chosen by the at-least-one rule are grayed.
http://ward.dojo.fed.wiki/assets/pages/sudoku-helper/sudoku.html HEIGHT 520
There are many programs that solve sudoku, in many programming languages. One of them which is worth studying is Roger Hui's in J
See Also Sudoku Inventory