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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 gcd(testVariable1, testVariable2) :
  # Base Case
  if testVariable1 == testVariable2 :
    return testVariable1

  # Recursive Case
  if testVariable1 > testVariable2 :
    return gcd(testVariable1 - testVariable2, testVariable2)
  else :
    return gcd(testVariable1, testVariable2 - testVariable1)

# Driver Code
number1 = 6
number2 = 9
print(gcd(number1, number2))

## Explanation
The **brute force** approach to finding $GCD$ of $2$ numbers would be to list all their divisors, pick the common divisors, and then select the greatest of them. However, a mathematical simplification can make this task easier.

The process of calculating $GCD$ is as follows:
If $m>n$, then $GCD(m,n)$ is the same as $GCD(m-n,n)$. This statement is based on the premise that if $m/d$ and $n/d$ both leave no remainder, then $(m-n)/d$ also leaves no remainder. 

This leads to the following algorithm:
$$
gcd(m,n) = \begin{cases} 
m \:\:\:\:\:\:\:\:\:\:\: if \:m == n, \\
gcd(m-n, n) \:\:\:\:\: if \:m > n, \\
gcd(m, n-m) \:\:\:\: if \:m < n,
\end{cases}
$$

Let's take a look at the code execution:



This review provides a detailed analysis of the solution to find the greatest common divisor.


Recursion Fundamentals

Iteration Vs. Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Solution Review: Find the Greatest Common Divisor

Solution: Using Recursion

Explanation