001 Multiples of 3 and 5.sf

#!/usr/bin/ruby

# Author: Daniel "Trizen" Șuteu
# License: GPLv3
# Website: https://github.com/trizen

# 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.

# https://projecteuler.net/problem=1

# Runtime: 0.151s

var N = 1000

# Solution 1
say N.range.grep{ (_ %% 3) || (_ %% 5) }.sum;

# Solution 2 (closed-form)
say (sum(^N `by` 3) + sum(^N `by` 5) - sum(^N `by` 15))