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

# What does the sum of integers from 1 to $n$ mean?

Natural numbers are all **positive numbers** starting with $1$. These can be written as follows:

$1,2,3,4,5,6,7,8,9,10......$

We want to write a program that takes a specific number and adds all the numbers from $1$ until that number.

For example, if $n = 5$, the sum of numbers from $1$ to $5$ is:
$1 + 2 + 3 + 4 + 5 = 15$.

## Mathematical Notation
Let's write it down mathematically:

$\sum_{i=1} ^{5} i$ 

$=$ $5$ $+$ $\sum_{i=1} ^{4} i$ 

$=$ $5$ $+$ $4$ $+$ $\sum_{i=1} ^{3}$ 

$=$ $5$ $+$ $4$ $+$ $3$ $+$ $\sum_{i=1} ^{2}$ 


.

.

.

$=5+4+3+2+1$


### Generic Mathematical Notation
$\sum_{i=1} ^{n} i$

$=$ $n$ $+$ $\sum_{i=1} ^{n-1} i$ 

$=$ $n$ $+$ $(n-1)$ $+$ $\sum_{i=1} ^{n-2}$ 

.

.

. 

$=$ $n$ $+$ $(n-1)$ $+(n-2)$ $ ... +2+1$ 

# Implementation

In this lesson, we will learn how to find the sum of numbers from 1 to n using recursion.



Recursion Fundamentals

Iteration Vs. Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Conclusion

Sum of Integers from 1 to n

What does the sum of integers from 1 to $n$ mean?

Sum of Integers from 1 to n

What does the sum of integers from 1 to nnn mean?

What does the sum of integers from 1 to $n$ mean?