Backtracking algorithm vs Norvig algorithm which is implemented here http://norvig.com/sudoku.html in python.
I runned both algos with hardest 95 sudoku puzzles.
This is the result
norvig:87 backtracking: 5 total time (ms):352 vs 55882
Norvig algorithm is most of the time faster than backtracking. In search() function of norvig, every recursive call must be called with deep copy of values.
Every recursive call must use its own independent parameter. (HashMap<String, String> values)