# Problem Solving: Computing GCD

Learn to write an efficient program that calculates the greatest common divisors of integers

## We'll cover the following

In mathematics, the **greatest common divisor (GCD)** of two or more integers, is the largest positive integer that divides each of the integers.

For example,

**Divisors of 8:** 1, 2, **4**, 8

**Divisors of 16:** 1, 2, **4**, 8, 16

**Divisors of 12:** 1, 2, 3, **4**, 6, 12

The GCD of **8**, **16** and **12** is * 4* because it is both a common divisor to each of them and the greatest of their common divisors. Sometimes, it is also called the

**highest common factor (HCF)**.

In this lesson, we will start with the most obvious solution and then tweak it till we get an efficient one. So let’s start!

## Finding the GCD of two numbers

We need to determine the biggest number that divides the two numbers. We can make a function (let’s call it `gcd()`

) that takes two integers `n1`

, and `n2`

and determines the greatest number, which divides both numbers.

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