There are usually two different sets of techniques for solving sudoku puzzles, namely "Direct Elimination Techniques" and "Candidates Elimination Techniques".
Direct Elimination Techniques, is a collection of techniques to determine the number for an unfilled cell directly by logically analyzing existing filled numbers and their relationship in the puzzle. It is composed of a set of simple algorithms, so that it is used mostly to solve puzzles of moderate difficulty levels or levels below.
Candidates Elimination Techniques, is another set of techniques to fill in all blank cells with tentative possible numbers, and then to remove candidates based on elimination techniques until a sole candidate is found. This kind of techniques is well developed and more and more new techniques are added to make it powerful enough to solve tough puzzles. Moreover, it is easier to be programmed.
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