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

# Problem Statement
Implement a function that takes a variable `testVariable` and finds the number that is placed at that index in the *Fibonacci sequence*.

## What is the Fibonacci Sequence?

The Fibonacci sequence is one of the most famous sequences in mathematics. Each number in the sequence is the sum of the two numbers that precede it.

So, the sequence goes:

$ 0, 1, 1, 2, 3, 5, 8, 13, 21, 34 ..... $ 

> Indexing starts at $0$. Therefore, at index $0$ we have the element $0$, at index $1$ we have the element $1$, at index $2$ we have the element $1$, and so on.

### Generic Mathematical Notation of Fibonacci Sequence
Any number, at index $n$ in the series, can be calculated using the following equation:

$F$n $=F$n-2$+F$n-1

By default, the *first** and the *second* number in the sequence are $0$ and $1$

$F$0 $= 0$

$F$1 $= 1$

$F$2 $=F$0$+F$1
 $=0 + 1= 1$

$F$3 $=F$1$+F$2
 $=1 + 1= 2$

$F$4 $=F$2$+F$3
 $=1 + 2= 3$

$F$5 $=F$3$+F$4
 $=2 + 3= 5$

$F$6 $=F$4$+F$5
 $=3 + 5= 8$

$F$7 $=F$5$+F$6
 $=5 + 8= 13$

Below is a visualization for the computation of the first $8$ elements in the Fibonacci sequence:

Given an index, find the nth Fibonacci number.

Recursion Fundamentals

Iteration Vs Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Challenge 3: The nth Fibonacci Number

Problem Statement

What is the Fibonacci Sequence?