Recursion

Recursion is a programming technique in which a function calls itself. If the problem can be divided into smaller versions, the function can call itself with these smaller subproblems. The concept of dividing a problem into smaller versions of itself is not uncommon, and we have come across it several times in school math, for instance. Let’s take an example.

A factorial of a number N, denoted by N!, is a product of all positive integers less than or equal to N. 4! would be 4 x 3 x 2 x 1.

Can you represent factorial in terms of a smaller version of itself? Can you identify a factorial of a number smaller than 4 in 4 x 3 x 2 x 1.

4! is simply 4 x 3!.

Each recursive call tackles a simpler version of the original problem. This process continues until a base case is reached, which is a simple condition that can be solved directly without further recursion. What do you think is the base case of factorial? Factorial of 1 is 1.

Factorial example

Here's a simple recursive implementation of a factorial function in Python.