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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

def average(testVariable, currentIndex = 0) : 
	# Base Case
	if currentIndex == len(testVariable) - 1 : 
		return testVariable[currentIndex] 
	
  # Recursive case1
	# When currentIndex is 0, divide sum computed so far by len(testVariable). 
	if currentIndex == 0 : 
		return ((testVariable[currentIndex] + average(testVariable, currentIndex + 1)) / len(testVariable)) 
	
  # Recursive case2
	# Compute sum 
	return (testVariable[currentIndex] + average(testVariable, currentIndex + 1)) 

# Driver code 
arr = [10, 2, 3, 4, 8, 0] 
print(average(arr)) 

## Explanation

> The average of an array containing only $1$ number, is the number itself. This condition can be our **base case**. 
$$
\displaystyle average \: of \: array \: of \: length \: 1={\frac {a_{0}}{1}} = a_{0}
$$

For the **recursive case** we have two conditions:
1. If the `currentIndex == 0`.
   * We have accumulated the **sum** of all the numbers of the array. Now, we **divide** that total sum with the length of the array.

2. If the `currentIndex != 0`.
   * We continue accumulating the sum of the numbers of the array.

In each recursive call, we move the `currentIndex` one step ahead.

This means that we reduce the length of the array with each step. When the length of the array reaches $1$, we add all the numbers in the reverse order. When we have added all the numbers, in the last step, i.e. when `currentIndex == 0`, we divide the total sum by the length of the array.

Let's take a look at the sequence of function calls for this example:

This review provides a detailed analysis of the solution to find the average of numbers.

Recursion Fundamentals

Iteration Vs. Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Solution Review: Average of Numbers

Solution: Using Recursion

Explanation