Exercise: Implement a Reverse Polish notation calculator Create an RPNCalculator class which can evaluate expressions written in Reverse Polish notation. It should have an evaluate instance method which takes as its input a valid RPN expression and returns its evaluation. Your calculator only needs to handle addition, multiplication, and subtrac…

rpncalculator.rb

class RPNCalculator

  def evaluate(expression)
    array = expression.split(' ')

    until array.length == 1
      array.each_with_index do |item, index|
        if item == "+" || item == "*" || item == "-"
          array[index] = eval(array[index - 2] + array[index] + array[index - 1]).to_s

          array.delete_at(index - 1) 
          array.delete_at(index - 2)
        end
      end  
    end

    array.join.to_i
  end  
end