The ultimate guide to recursion interviews in JavaScript. Developed by FAANG engineers. Practice with real-world interview questions and get interview-ready in just a few hours.

If you’ve ever struggled with solving problems using recursion, or if you have to brush up your skills for an interview, this course is for you.

We'll start with the basics of what recursion is and why it’s important before diving into practicing solving actual questions. 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 to solve complex real-world problems. We hope that through practicing recursion, you will be able to ace all recursion related questions in interviews at top tech companies.

Recursion for Coding Interviews in JavaScript

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

**Natural numbers** are positive numbers starting from $1$. These can be written as:

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

We want to write a program that takes a number and sums up all the numbers from $1$ up to that number.

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

## Mathematical Notation
The sum of all numbers up to a number is equal to the sum of that number and the sum of all the numbers before it. 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'll learn how to find the sum of numbers from 1 to n.

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?