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

# What does “Count all Occurrences of a Number” mean?

Our task is to find the number of times a key occurs in an array.

For example:

## Explanation

We need to count the number of times `key` occurs in an array. 

We do this by:
1. Checking the first element. 
2. If the first element is the specified `key`, we will add $1$ to the result. 
3. Else, add $0$ to the result. 
4. After checking the first element, remove it, and call the function `count` again on the rest of the array.

> Remember, it is easier to implement recursive code if we visualize the solution of the larger problem as the sum of the solution to the smaller tasks. 

Let's visualize the solution to this problem:


In this lesson, we will learn how to count all occurrences of a key in a given array.

Recursion Fundamentals

Iteration Vs Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Count all Occurrences of a Number

What does “Count all Occurrences