The ultimate guide to recursion interviews. Developed by FAANG engineers, practice with real-world C++ problems, interactive code playgrounds, and get interview-ready in just a few hours.

If you’ve ever struggled with solving coding problems using recursion, or if you’ve just got an interview coming up and want to brush up on your knowledge, you’ll definitely find this course helpful.
 
You’ll start with the basics of what recursion is and why it’s important before diving into what it looks like in practice. You’ll see how recursion can help you solve a variety of different math, string, and data structure problems, using interactive code playgrounds you can execute directly in your browser. You’ll have access to detailed explanations and visualizations for each problem to help you along the way.  
 
By the time you’re done, you’ll be able to use what you’ve learned to solve complex real-world problems, and even advance more easily through your interviews at top tech companies.

Recursion for Coding Interviews in C++


# What is a factorial?
A factorial is the product of an integer and all the positive integers less than it. It is denoted by the symbol: $!$

For example, 4! (read as four factorial) is denoted as follows:

$4!=4\times3\times2\times1=24$

$6!=6\times5\times4\times3\times2\times1=720$


## Expanding a Factorial
A factorial of any integer can be written as a product of that integer and the factorial of the integers less than it. For example, $6!$ can be written as follows:  

$6!=6\times5!$  

$6!=6\times5\times4!$

$6!=6\times5\times4\times3!$

$6!=6\times5\times4\times3\times2!$

$6!=6\times5\times4\times3\times2\times1$


> **Important Note:** Factorials only exists for positive numbers. The factorial of 0 is equal to 1. 

## Mathematical Notation
The factorial of a number can be written in the  form shown below:

$n!=n\times(n-1)!$

The generic mathematical notation for computing a factorial is:

$n!=(n)\times(n-1)\times(n-2)\times(n-3)\times(n-4)....(3)\times (2)\times(1)$
 
**We will now use the recursive function concept for computing the factorial of a number.**


In this lesson, we will use recursion to solve the basic mathematical problem of computing a factorial.

Recursion Fundamentals

Recursion with Numbers

Recursion With Strings

Recursion With Arrays

Recursion with Data Structures

Computing Factorials

What is a factorial?

Expanding a Factorial