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@fabianuribe
Created Jul 23, 2013
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RPN
# 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 subtraction (not division).
# Operators and numbers should be separated by a single space.
# For example,
# 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 )
#
#
# Implement an RPN calculator that takes an expression like
# 19 2.14 + 4.5 2 4.3 / - *
# which is usually expressed as (19 + 2.14) * (4.5 - 2 / 4.3)
class RPNCalculator
def initialize
@array = Array.new
@stack = Array.new
end
def evaluate(string)
@array = string.split
@array.each do |x|
if x.match(/(\d+)/)
@stack << x.to_i
else
case x
when '+'
@stack << @stack.pop + @stack.pop
when '-'
@stack << - @stack.pop + @stack.pop
when '*'
@stack << @stack.pop * @stack.pop
end
end
end
return @stack.join.to_i
end
end
calculator = RPNCalculator.new
#Test operation :Should print : 0
p calculator.evaluate("70 10 4 + 5 * -")
p calculator.evaluate("12 2 3 + *")
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