The ultimate guide to recursion interviews with strategies developed by FAANG engineers. Practice with real-world interview questions, detailed explanations, and visualizations to prep faster.

If you’ve got an interview coming up and want to brush up on your knowledge, or if you’ve ever struggled with solving coding problems using recursion, you'll 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 by using interactive code playgrounds that 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 Java

## Understanding the Problem

You should now have a clear understanding of how recursion works - what it is and when it can be used. Before you proceed writing your own recursive code, it is very important to understand the nitty-gritty details of how the code actually works.

Below is a basic example of how the order of execution for a recursive method changes at each successive recursive call.



### Example

What do you think is the output of the code below? Take your time to think it over before you execute the code and look at the result.

class ExampleClass {

    private static void printNum(int n) {
        // Base case
        if (n == 0) {
            return;
        }
        // Recursive case
        printNum(n-1);
        System.out.print(n + " ");
    }

    public static void main( String args[] ) {
        // Recursive method called here
        printNum(6);   
    }
}

### Code Explanation

If we read the method as it is written, we might expect the output to be $6, 5, 4, 3, 2, 1$. Doesn't it seem like the method prints 6 first and then gradually gets decremented?

Sadly, this is not correct. We have to *evaluate the recursive call before we can continue to the end of the method*.

The code snippet below illustrates how the code gets executed.

# Understanding the Problem

You should now have a clear understanding of how recursion works - what it is and when it can be used. Before you proceed writing your own recursive code, it is very important to understand the nitty-gritty details of how the code actually works.

Below is a basic example of how the order of execution for a recursive method changes at each successive recursive call.



## Example

What do you think is the output of the code below? Take your time to think it over before you execute the code and look at the result.

## Code Explanation

If we read the method as it is written, we might expect the output to be $6, 5, 4, 3, 2, 1$. Doesn't it seem like the method prints 6 first and then gradually gets decremented?

Sadly, this is not correct. We have to *evaluate the recursive call before we can continue to the end of the method*.

The code snippet below illustrates how the code gets executed.

In this lesson, we will go deep into understanding a recursive problem.

Fundamentals of Recursion

Iteration to Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Understanding a Recursive Problem

Understanding the Problem

Example

Code Explanation