The ultimate guide to coding interviews. Developed by FAANG engineers. Boost problem-solving skills with number theory, dynamic programming, and graph theory. Get interview-ready in just a few hours.

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Whether you’re gearing up for online coding challenges, code-a-thons, or interviews, then this course is for you. With this course, you will solidify your problem-solving skills ensuring a swift sail through any problem. 


You will be tasked with solving some of the most frequently asked questions that are brought up in FAANG interviews. You will start with the concepts of Number Theory and Divide and Conquer, and gradually move towards more complex problems like dynamic programming and graph theory.


With each problem you solve, there will be insightful explanations and full implementation details to really hammer home the concepts. By the time you finish this course, you will have the confidence to solve any problem, no matter the difficulty.

Competitive Programming - Crack Your Coding Interview, C++

# Introduction
Euler’s Phi function (also known as totient function, denoted by $\phi$) is a function on natural numbers that gives the count of positive integers co-prime with the corresponding natural number, i.e., the numbers whose GCD (Greatest Common Divisor) with **N** is **1**. So we can say the following:

$\phi$(1) = 1 because *gcd(1, 1) is 1.*

$\phi$(2) = 1 because *gcd(1, 2) is 1, but gcd(2, 2) is 2.*

$\phi$(3) = 2 because *gcd(1, 3) is 1 and gcd(2, 3) is 1.*

$\phi$(4) = 2 because *gcd(1, 4) is 1 and gcd(3, 4) is 1.*

$\phi$(5) = 4 because *gcd(1, 5) is 1, gcd(2, 5) is 1, gcd(3, 5) is 1 and gcd(4, 5) is 1.*

$\phi$(6) = 2 because *gcd(1, 6) is 1 and gcd(5, 6) is 1.*

# Solution
The value $\phi$(n) can be obtained by Euler’s formula. It basically says that the value of $\phi$(n) is equal to `n` multiplied by product of *(1 – $\frac{1}{p}$)* for all prime factors `p` of `n`. For example, the value of $\phi$(6) *= 6 * (1-$\frac{1}{2}$) * (1 – $\frac{1}{3}$) = 2.*

Now, let us look at the implementation of this function.

Learn about the Euler Phi's function that can be used to solve many coding problems.

Overview

Number Theory

Number Theory

Divide and Conquer

Greedy Algorithms

Greedy Algorithms

Recursion and Backtracking

Recursion and Backtracking

Dynamic Programming

Graphs

Bonus Lessons

Euler Phi's Function

Introduction