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 sum35(n)
  (1...n).select{|i|i%3==0 or i%5==0}.sum
end
puts sum35(1000)      #=> 233168