This sudoku solver implements Donald Knuth’s dancing links algorithm to solve sudoku puzzles quickly. Dancing links is an algorithm for solving exact cover problems, which include Sudoku and the N queens problem.
The implementation averaged about 1.5 ms on 15 high difficulty (human rated) sudoku puzzles I found online.
References
Knuth, D. E. (2000). Dancing links. ArXiv:Cs/0011047. http://arxiv.org/abs/cs/0011047