Task

The objective is to write a function that finds the sum of all positive multiples of 3 or 5 below n.

Show output for n = 1000.

This is is the same as Project Euler problem 1.

Extra credit: do this efficiently for n = 1e20 or higher.




def sumMul = { n, f -> BigInteger n1 = (n - 1) / f; f * n1 * (n1 + 1) / 2 }
def sum35 = { sumMul(it, 3) + sumMul(it, 5) - sumMul(it, 15) }