The ultimate recursion guide! Master basics, solve real-world problems, and get interview-ready in hours with FAANG engineers’ proven strategies.

If you’ve ever struggled with solving coding problems using recursion, or if you need to brush up your recursion skills for an interview, this course is for you! We will start with the basics of recursion before we practice solving actual coding problems. 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 of recursion to solve complex, real-world problems. We hope that this course will help you ace all the recursion related questions during interviews at top tech companies!

Recursion for Coding Interviews in Python

# Understanding the Problem
In the previous lessons, we learned the basic concept of recursion and its uses. Now, we will discuss how recursion works.

Let's take a look at an example code:

def printPattern(targetNumber) :
  
  if (targetNumber <= 0) :
    print(targetNumber)
    return

  print(targetNumber)
  printPattern(targetNumber - 5)
  print(targetNumber)

# Driver Program 
n = 10
printPattern(n)

On first glance, we notice that the `targetNumber` is decreased by $5$ and `printPattern()` is being called again. However, there are two `print()` statements preceding and succeeding the recursive call. 

## Code Explanation
We want to print a pattern:
$10$ $5$ $0$ $5$ $10$.
Notice, we first decrease the `targetNumber` by $5$ then increase the `targetNumber` by $5$. However, the middle number (0) is printed only once.

Therefore, this becomes our **base case**:
```python
if targetNumber <= 0:
  print targetNumber
  return
```

Now, the remaining numbers are printed twice on each side of the base case.
```python
print targetNumber
printPattern(targetNumber - 5)
print targetNumber
```
This is our recursive case.


There are three methods commonly used to process the code flow of a recursive program and to **dry run** the code:

# Visualizing Through a Stack
The concept of a stack is critical in recursion. The concept of recursive calls and their outputs are easier to understand when you visualize your function calls through a stack.

Let's revisit this concept with an example:

In this lesson, we will go over methods to help you visualize a recursive function.

Recursion Fundamentals

Iteration Vs. Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Understanding a Recursive Problem

Understanding the Problem