無題

#!/usr/bin/rubyclass Stack  def initialize()    @stack = [];  end  def push(value)    @stack.push(value)  end  def pop()    @stack.pop()  end  def peek()    @stack.last()  end  def empty?()    @stack.empty?()  endendwhile gets  priority = {"*" => 2, "/" => 2, "+" => 1, "-" => 1, "(" => 0, ")" => 0}  input = $_  output = ""  stack = Stack.new()  input.scan(/\d+|[\+\-\*\/\(\)]{1}?/).each{ |token|    case token    when "+","-","*","/"      output << stack.pop() + " " while not stack.empty?() and priority[stack.peek()] >= priority[token]      stack.push(token)    when "("      stack.push("(")    when ")"      output << stack.pop() + " " until stack.peek() == "("      stack.pop()    else      output << token + " "    end  }  output << stack.pop() + " " until stack.empty?()  print output.strip + "\n"end