The ultimate guide to recursion interviews with strategies developed by FAANG engineers. Practice with real-world interview questions, detailed explanations, and visualizations to prep faster.

If you’ve got an interview coming up and want to brush up on your knowledge, or if you’ve ever struggled with solving coding problems using recursion, you'll find this course helpful.
 
You’ll start with the basics of what recursion is and why it’s important before diving into what it looks like in practice. You’ll see how recursion can help you solve a variety of different math, string, and data structure problems by using interactive code playgrounds that you can execute directly in your browser. You’ll have access to detailed explanations and visualizations for each problem to help you along the way.  
 
By the time you’re done, you’ll be able to use what you’ve learned to solve complex real-world problems and even advance more easily through your interviews at top tech companies.

Recursion for Coding Interviews in Java

# 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 particular number and sums up all the numbers from 1 up until that number. 

The illustration below explains the concept to help you understand.



The sum of all numbers up to a particular number is equal to the sum of that number and the sum of all the numbers before it. It can be seen as follows:

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

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

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

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

.

.

.

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


## 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$ 

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

Fundamentals of Recursion

Iteration to Recursion

Recursion with Numbers

Recursion with Strings

Recursion with Arrays

Recursion with Data Structures

Sum of Integers from 1 to n

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