I've seen a few other solvers out there - this a processing / java version that uses Knuth's dancing links, and some pre-pruning and feasibility checks (DLX doesn't readily allow all the constraints to be converted into a sparse matrix for solving). Generally finds a solution for any given puzzle in a few milliseconds. Or up to 1.5-2 seconds to get all solutions for some of the larger puzzles, depending on the constraints (the hardest puzzle so far has 2.764m possible solutions)