Week4

Recursion is not a new thing but actually everyone who's never known it before really need a long time to get used to it. Most people like to read a recursive function by tracing it step by step, using a stack or something like that. Of course, it is the easiest way to do it. But we still got other ways. Because of the recursiveness, we can try to understand the basic part of a recursive function, and then repeat it over and over in our mind to get to the final result.