calculator.rb

#http://www.codewars.com/dojo/katas/5235c913397cbf2508000048/discuss/ruby
class Calculator
  def evaluate(string)
    groups_of_operators = [["/", "*"], ["-", "+"]]
    arr = string.split
    groups_of_operators.each do |group|
      (0..arr.size).each do |i|
        if group.include?(arr[i+1])
          arr[i+1] = arr[i].to_i.send(arr[i+1], arr[i+2].to_i)
          arr.delete_at(i+2)
          arr.delete_at(i)
        end
      end
    end
    arr[0].to_i.send(arr[1], arr[2].to_i)
  end
end