I recently started working on the #projecteuler100 challenge, and I thought I would share how I solved the problems on here. Here’s a complete walkthrough to Project Euler problem 1.

Note: I’ve written all of my solutions in Java, but the concept is the same in any language.

## Project Euler Problem 1

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

You can view my solution to this problem here.

To get started with problem 1, we first need a loop that will iterate over every number from 0 to 1000 (This is because Project Euler problem 1 states we want to find all of the multiples of 3 or 5 below 100. You can implement this in a variety of ways, but I chose to use a simple for-loop. We also need some kind of variable that will hold our sum.

int sum;
for (int i = 0; i < 1000; i++) {

}

Within the for loop, we want to check if the number is divisible by either 3 or 5. If it is, we then want to add that number to the sum. To check for divisibility, we can just use the modulus operator to check for a remainder of 0.

if (i % 3 == 0 || i % 5 == 0) {
sum += i;
}

Finally, we can output the sum of all the values to the console.

System.out.println(sum);

Read up on other Project Euler solutions on the project euler category of this website.