Summary

Recursion occurs whenever a routine calls itself, directly or indirectly, as part of its processing. One or more base cases are needed to end the recursion; otherwise, the algorithm loops indefinitely - a common problem to watch out for.

A recursive algorithm can always be recoded to use iteration in place of recursion by using a stack to maintain the algorithm’s state, which is essentially what the program is doing anyway. Sometimes, however, an iterative alternative to a recursive algorithm can be found, and such solutions are generally more efficient than their recursive counterparts.