Norvig has some great solutions. However I have still yet to see something that can beat a well coded dancing (http://www.ocf.berkeley.edu/~jchu/publicportal/s

Norvig has some great solutions. However I have still yet to see something that can beat a well coded dancing (http://www.ocf.berkeley.edu/~jchu/publicportal/sudoku/sudoku.paper.html http://www.ocf.berkeley.edu/~jchu/publicportal/sudoku/sudoku... http://en.wikipedia.org/wiki/Dancing_Links http://en.wikipedia.org/wiki/Dancing_Links) links solution to Sudoku, for speed. For my money, giving humanistic solutions for sudoku is the more interesting problem. The size of the search space is so constrained that a correctly coded solution will finish so quickly that it's no longer an interesting race. Rating puzzles for how much trouble a real person will have solving is also very interesting.