If we build an engine for a car or anything else, it almost always is going to have some key element that's operating in a cycle, otherwise it won't keep going, right.

如果我们为一辆汽车，或其他什么东西制造一台引擎,它总要有一些关键，要素来形成循环。

麻省理工公开课 - 热力学与动力学课程节选

Because if you did what I suggested with the list, the time to look up the key would be linear in the length of the list. You'd have to look at each element until you found the key.

字典是用一种很神奇的，叫做散列法的算法,来实现的，后面我们将,会学到一点关于。

麻省理工公开课 - 计算机科学及编程导论课程节选