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

Question

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. I have the following code but the answer do

Answer 1

Think declaratively - what you want to do, rather than how you want to do.

In plain language, it boils down to exactly what the problem asks you to do:

1. Find all multiples of 3 or 5 in a certain range (in this case 1 to 1000)
2. Add them all up (aggregate sum)

In LINQ, it looks like:

Enumerable.Range(1, 1000)
            .Where(x => (x % 3 == 0) || (x % 5 == 0))
            .Aggregate((accumulate, next) => accumulate += next);

Now, you can convert this into an iterative solution - but there is nothing wrong with using a declarative solution like above - because it is more clear and succinct.