gistfile1.txt

square:~/code/euler[master]% ruby problem1.rb --solution
Project Euler
Problem 1
=============
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.
Solution (calculating): 
266333

problem1.rb

require "project_euler"

problem = Euler::Problem.new(1, <<DESCRIPTION
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.
DESCRIPTION
)

def sum_multiples_of(num, up_to=1000)
  multiples = []
  i = 1
  multiple = 0
  until multiple >= up_to
    multiple = num * i
    multiples << multiple if multiple < up_to
    i += 1
  end

  #puts multiples.inspect

  sum_of_multiples = multiples.inject { |sum, n| sum + n }
end

problem.solve { sum_multiples_of(3, 1000) + sum_multiples_of(5, 1000) }