Note the caching is not really required for the particular traversal algorithm you are using, but I leave it in to show how to do this if it is needed as you expand this tool in the future.
注意，这个缓存对于您使用的特定遍历算法并不真正需要，我在这里使用它只是为了展示当您将来需要扩展这个工具时应该怎样做。
It never earned me a living. For that I had to do other things-when I really needed money, for my wife and kids.
可是买来的学位从来不能帮我养家糊口，我需要钱来养老婆孩子，不得不做些别的营生。
It also helped convince me that there were some really good practices that I needed to learn.
这本书帮助我确定了有一些很好的实践我应该去学习。
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