Project Euler: Problem 1


Recently I decided that my brain needed some exercise. So I figured I would try to solve a couple of Project Euler problems once in a while. And while I was at it, try to to do a bit of TTD, or at least write test cases for things. What is Project Euler? Well, here is some of what they say about themselves, whoever they are:

Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.

The motivation for starting Project Euler, and its continuation, is to provide a platform for the inquiring mind to delve into unfamiliar areas and learn new concepts in a fun and recreational context.

I'm not particularly good at these things, but it is quite fun when you get it right. I also get to practice my Google-Fu a bit when I need to freshen up things I learned during math at school, but have forgotten. Or if I find that my solution to a problem is totally awful and takes ages to solve...

Anyways, I can recommend the problems so far. They have (so far) been mind bending enough to be challenging, but not so insanely difficult that they are impossible.

The first problem goes like this:

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.

Project Euler Problem 1

To solve this problem I used a pretty straight forward LINQ statement. It basically just generates all the numbers from 0 to 999, filters out the numbers not dividable by 3 or 5, and then sums those up.

var multiples = new long[] {3, 5};
var answer =  Enumerable
  .Range(0, 1000)
  .Where(x => multiples.Any(y =>; x%y == 0))

The answer to that would then be 233168, and it the code took less than 10 milliseconds to find.

So, how did you solve it? What do you think about my solution?