在对波兰表达式进行运算，严格按照自左至右的顺序进行 。下面给出一些表达式及其相应的波兰表达式 。
表达式 波兰表达式 A- 。
7. 如何设计算法 设计一个正确的算法是一件困难的工作，因为它需要创新，从以太真空中发掘出一个解方案来解决问题 。
算法设计比对现有的方案进行改良要难得多，因为算法设计的可选择空间太，过多的自由反而成了一种约束 。This book is designed to make you a better algorithm designer. The techniques presented in Part I of this book provide the basic ideas underlying all combinatorial algorithms. The problem catalog of Part II will help you with modeling your application and point you in the right direction of an algorithm or implementation. However, being a successful algorithm designer requires more than book knowledge; it requires a certain attitude, the right problem-solving approach. It is difficult to teach this mindset in a book; yet getting it is essential to become a successful designer. 本书的设计目标是让你成为一个更好的算法设计者 。
本书第一部分展示有关组合算法的基本原理和基本思想；第二部分的问题清单帮助你为你的问题建模，并且为你指明实现正确算法的方向 。尽管如此，要成为一个成功的算法设计者光有书本知识是不够的，面对问题的态度（attitude）和选择正确的方法更重要 。
书本容易传授知识，很难传授人的心态（mindset）和思考方式；而这种心态和思考却是成为成功的算法设计者的根本条件 。The key to algorithm design (or any other problem-solving task) is to proceed by asking yourself a sequence of questions to guide your thought process. What if we do this? What if we do that? Should you get stuck on the problem, the best thing to do is move onto the next question. In any group brainstorming session, the most useful person in the room is the one who keeps asking, ``Why can't we do it this way?'' not the person who later tells them why. Because eventually she will stumble on an approach that can't be shot down. 算法设计（或其它问题解决任务）的关键是一系列持续的自我反问，这些反问引导我们思维的前进 。
“如果这样做会怎样？”，“如果那样做又会怎样？”……如果 你被一个问题掐住了，最好的办法就是先搁一下，换一个问题换一个前进的方向试试 。在每组头脑风暴会议中，最有价值的人是不断提出为什么的人，不是尔后解说为什么的人 。
因为我们常常被一些习以为常的东西所拌倒，掉进自己设置的陷阱 。kemin：如果问题解决是一种思考过程，那么思考的形式（过程的严谨性、细致性和正确性）很重要，而思考的内容也不容忽视 。
因为引导我们思考前进的方式 除反问本身外，反问的内容也很重 。就比如参加头脑风暴的材料一样 。
人大脑的思维功能是硬编码的，人与人之间没有思维规律——质的区别，只是思维的清晰度和 灵敏度——量的差别 。人与人之间智力的差别更多体现在思维内容的量上，体现在对外部世界的事实掌握的广度和深度上 。
Towards this end, we provide below a sequence of questions to guide your search for the right algorithm for your problem. To use it effectively, you must not only ask the questions, but answer them. The key is working through the answers carefully, by writing them down in a log. The correct answer to, ``Can I do it this way?'' is never ``no,'' but ``no, because。.'' By clearly articulating（明确有力地表达） your reasoning as to why something doesn't work, you can check if it really holds up or whether you have just glossed（掩盖） over a possibility that you didn't want to think hard enough about. You will be surprised how often the reason you can't find a convincing（使人信服的） explanation for something is because your conclusion is wrong. 在末尾我们提供一个反问问题的列表，你不但要反问自己这些问题，更重要是仔细回答这些问题，最好把答案写下来 。