problem-005.rb

#!/usr/bin/env ruby

# What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20

# The divisors are limited because there is no need to check disivion by all the numbers
# from 1 to 20. For eg. if number is divisible by 18, we know it's all divisible by 2, 3, 6 and 9

# There is a chance to cut some run time by changing the order of the divisors.

def divisible_by_1to20?(number)
  divisors = [19, 18, 17, 16, 15, 14, 13, 12, 11]
  divisors.each do |n|
    if (number%n != 0)
      return false
    end
  end
  return true
end

number, base = 20, 1
until divisible_by_1to20?(number)
  number = base*20
  base += 1
end

puts "Answer: #{number}"