# Recursion Summary

In this module, we explored the use of recursion to write concise solutions for a variety of problems. Recursion allows us to call a function from within itself, using either head recursion, tail recursion or tree recursion to solve smaller instances of the original problem.

Recursion requires a base case, which tells our function when to stop calling itself and start returning values, and a recursive case to handle reducing the problem’s size and calling the function again, sometimes multiple times.

We can use recursion in many different ways, and any problem that can be solved iteratively can also be solved recursively. The power in recursion comes from its simplicity in code—some problems are much easier to solve recursively than iteratively.

Unfortunately, in general a recursive solution requires more computation time and memory than an iterative solution. We can use techniques such as memoization to greatly improve the time it takes for a recursive function to execute, especially in the case of calculating Fibonacci numbers where subproblems are overlapped.