Reverse Polish Calculator first implementation

burbank_rpn.rb

#calc = RPNCalculator.new

#calc.evaluate('1 2 +')   # => 3
#calc.evaluate('2 5 *')   # => 10
#calc.evaluate('50 20 -') # => 30

# The general rule is that 'A B op' is the same as 'A op B'
# i.e., 5 4 - is 5 - 4.
#calc.evaluate('70 10 4 + 5 * -') # => 0

#70 10 4 + 5 * - == 70 -(14 *5) == 0

class RPNCalculator
	
	def evaluate(x)
		array = x.split(" ")
		
		array.map! do |a|
			if a == "+" || a == "-" || a == "*"
				a 
			else
				a = a.to_i
			end
		end
		
		stack = []
		operation = 0
				
		array.each_index do |var| 
		 	if array[var].class == Fixnum
		 	stack << array[var]
		 	else
		 		if array[var] == "*"
		 			operation = stack[-1] * stack[-2]
		 			stack.pop(2)
		 			stack.push(operation)
		 		elsif array[var] == "+"
		 			operation = stack[-1] + stack[-2]
		 			stack.pop(2)
		 			stack.push(operation)
		 		else 
		 			operation = stack[-2] - stack[-1]
		 			stack.pop(2)
		 			stack.push(operation)
		 		end
		 	end
		 end
		 return stack[0]

	end
end
calc = RPNCalculator.new
puts calc.evaluate('70 10 4 + 5 * -')