The ultimate guide to recursion interviews in JavaScript. Developed by FAANG engineers. Practice with real-world interview questions and get interview-ready in just a few hours.

If you’ve ever struggled with solving problems using recursion, or if you have to brush up your skills for an interview, this course is for you.

We'll start with the basics of what recursion is and why it’s important before diving into practicing solving actual questions. You’ll have access to detailed explanations and visualizations for each problem to help you along the way. 

By the time you have completed this course, you’ll be able to use all the concepts to solve complex real-world problems. We hope that through practicing recursion, you will be able to ace all recursion related questions in interviews at top tech companies.

Recursion for Coding Interviews in JavaScript

## Explanation
The naive approach to finding $GCD$ of $2$ numbers is to list all their divisors. Then pick the common divisors, and then select the greatest out of them.

However, an easy mathematical simplification can make our task easier.

The idea behind calculating $GCD$ is:
If $m>n$, $GCD(m,n)$ is the same as $GCD(m-n,n)$.

This is because if $m/d$ and $n/d$ both leave no remainder, then $(m-n)/d$ leaves no remainder, either. 

This leads to the following algorithm:
$$
gcd(m,n) = \begin{cases} 
m \:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\: if \:m == n, \\
gcd(m-n, n) \:\:\:\:\: if \:m > n, \\
gcd(m, n-m) \:\:\:\: if \:m < n
\end{cases}
$$

### Example1: Where m < n
Suppose $m = 42$ and $n = 56$.

* **Step1:** $m < n$, therefore, subtract $42$ from $n$.
Now, $m = 42$ and $n = 14$. 

* **Step2:** $m > n$, therefore, subtract $14$ from $m$.
Now, $m = 28$ and $n = 14$. 

* **Step3:** $m > n$, therefore, subtract $14$ from $m$.
Now, $m = 14$ and $n = 14$. 

* **Step4:** $m == n$, therefore, the greatest common divisor of $42$ and $56$ is $14$.

Let's have a look at the code execution:

This review provides a detailed analysis of the solution to find the greatest common divisor.

Recursion Fundamentals

Iteration Vs Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Solution Review: Find the Greatest Common Divisor

Solution: Using Recursion

Explanation