computers are hard

rpn calculator of doom

class RPNCalculator
  def evaluate(exp)
    exp_array = exp.split(" ").to_a
    rpn_array = []
    exp_array.each do |i|
      if i.match(/\d/) != nil
        rpn_array << i.to_i
      else
        rpn_array << i
      end
    end

    while rpn_array.length > 1

      rpn_array.length.times do |index|
        operator = rpn_array[index]

        case operator
        when "+", "-", "*"

          case operator
          when "+"
            result = rpn_array[index-2] + rpn_array[index-1]
          when "-"
            result = rpn_array[index-2] - rpn_array[index-1]
          when "*"
            result = rpn_array[index-2] * rpn_array[index-1]
          end

          rpn_array[rpn_array.index(operator)] = result

          rpn_array.delete_at(index-1)
          rpn_array.delete_at(index-2)

          break
        end
      end
    end
    rpn_array[0]
  end
end