What is recursion and when should I use it?

Answer 1

1.) A method is recursive if it can call itself; either directly:

void f() {
   ... f() ... 
}

or indirectly:

void f() {
    ... g() ...
}

void g() {
   ... f() ...
}

2.) When to use recursion

Q: Does using recursion usually make your code faster? 
A: No.
Q: Does using recursion usually use less memory? 
A: No.
Q: Then why use recursion? 
A: It sometimes makes your code much simpler!

3.) People use recursion only when it is very complex to write iterative code. For example, tree traversal techniques like preorder, postorder can be made both iterative and recursive. But usually we use recursive because of its simplicity.