Introduction - If you have any usage issues, please Google them yourself
Microsoft Surface questions: given a function to output a string of all order. Simple backtracking can be achieved. Of course, have also arranged a variety of algorithms, to look at the combination of mathematics, there is generated reverse order and some do not need to generate with recursive method. Knuth impression of depth inside <TAOCP> I spoke with the generation. Understanding of these algorithms need a certain degree of mathematical knowledge, also requires a certain degree of inspiration, are interested in to see the best.