RPN Calculator

gistfile1.rb

class RPNCalculator
  def initialize
  end
 
  def evaluate(rpn)
    expressions = rpn.split(' ')
    ans = []
    expressions.each do |obj|   # example: (5 1 2 + 4 * + 3 -)
      if obj.to_s[/[0-9]+/]
        
        ans << obj.to_i

      else ["*","+","-"].include?(obj) 

        operands = ans.pop(2)
        ans << (operands[0].send(obj,operands[1]))
      end
    end
  ans[0]
  end
end

puts calc = RPNCalculator.new
puts calc.evaluate('1 2 +') == 3   # => 3
puts calc.evaluate('2 5 *') == 10  # => 10
puts calc.evaluate('50 20 -') == 30 # => 30
puts calc.evaluate('70 10 4 + 5 * -') == 0 # => 0