Inside the suitcase is a plain piece of white paper and the children were asked to draw the things they think they would need on the trip. Sometimes they get they wouldn't need.

行李箱里面是一张普通的白纸,我要求孩子们,在纸上画出他们认为必要的,旅行用品，有时候他们画出来的并不需要。

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So binary search, the phonebook example, binary search on the pieces of paper on the white board, why is that?

是二分查找，例如电话簿的例子,对其中的某一页进行二分查找，为什么呢？

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