Euler problem 1

gistfile1.txt

# Brute force
sum = 0
(1..999).each do |num|
  sum = sum + num if (num % 3 == 0 || num % 5 == 0)
end
puts "Brute force: #{sum}"

# More rubyish, but still brute force
sum = (1..999).inject(0) {|sum,num| (num % 3 == 0 || num % 5 == 0) ? sum + num : sum}
puts "More rubyish but still brute force: #{sum}"

# Smart way
def divisible_sum(num, max)
  occ = max/num
  occ.to_f/2 * (num + (num * occ))
end

sum = divisible_sum(3, 1000) + divisible_sum(5, 1000) - divisible_sum(15, 1000)
puts "Smarter: #{sum}"