Sudoku puzzles are Assignment problems (http://en.wikipedia.org/wiki/Assignment_problem http://en.wikipedia.org/wiki/Assignment_problem), and can be cast as Gra

Sudoku puzzles are Assignment problems (http://en.wikipedia.org/wiki/Assignment_problem http://en.wikipedia.org/wiki/Assignment_problem), and can be cast as Graph Coloring problems as well (http://en.wikipedia.org/wiki/Graph_coloring http://en.wikipedia.org/wiki/Graph_coloring). Although the performances reported are more than good, the discussion on brute-force algorithms omits that some of the cutting-edge research on the topic is in the Constraint Programming community (Sudoku is the typical example of the "all-different" modeling constraint). One of the most commonly used algorithm used in Optimization (and in feasibility problems as well) is Branch and bound (http://en.wikipedia.org/wiki/Branch_and_bound http://en.wikipedia.org/wiki/Branch_and_bound). Combinatorial problems of that size are relatively small and can be solved in fractions of a second by off-the-shelf commercial software and very little modeling work.