Sudoku is pretty clearly an "exact cover" problem, and there are loads of known ways to attack those; Knuth's DLX being a particularly elegant one. As a gener

Sudoku is pretty clearly an "exact cover" problem, and there are loads of known ways to attack those; Knuth's DLX being a particularly elegant one. As a general principal, it's always a good idea to see if the problem you are facing resembles other known, solved problems.