In reply to phil192.
Hi Philip, that’s a very good question that I’ve been thinking through for some time.However, after reading a good article I found online, I learned that method is the best approach. After a certain number of cells removed though, it could create conflicts and lead to more than one solution as you mention. I will try to upload the excel (not sure if I can do it there in the blog), so that people can test. Please have a look at this article if you are interested in the different ways of generating and solving Sudoku puzzles::http://theinf1.informatik.uni-jena.de/publications/sudoku-weller08.pdf