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OK. Can we sort it in linear time? Hmmm.
恩，这个就不那么显然了。
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That one's not so obvious. So let's think about this for a second. To sort a list in linear time, would say, I have to look at each element in the list at most a constant number of times.
所以让我们来思考一会,要在线性时间能排序，列表里每个元素最多被使用常数次,不一定是一次，对吧。
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Does it make sense to think we could do this in less than linear time? You know, it takes a little bit of thinking. What would it mean do I see a hand way at the back, yes please? Thank you.
你要稍微想一想，这意味着什么？,那儿是有人举手么？后面的,请你来回答吧,谢谢你，小伙子,你让我体会到我上课的价值。
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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。
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Obviously-- and that's a bad way of saying it, I said constant the previous time-- in the linear case, it's subtract by certain amount.
这么描述很不准确，我之前在，线性算法中也说了常数,它是每次减少固定的量。
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Right? If that was the case in that code, then my complexity is no longer log, because I need linear access for each time I've got to go to the list, and it's going to Lisp be much worse than that.
这里的复杂度不再是对数的了，因为每次在列表中，查找需要线性访问,可能还要糟糕,其实，有些编程语言，如。
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Well let's see. My fall back is, I could just do linear search, walk down the list one at a time, just comparing those things. OK. So that's sort of my base. But what if I wanted, you know, how do I want to get to that sorted list? All right?
我只能做线性搜索了,一次遍历一遍列表，一个一个比较，但如果我想要,那怎样得到有序的列表呢？,现在的一个问题是，我们排序之前？
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We saw some quadratic algorithms, typically those are things with multiple nested loops, or iterative or recursive calls, where you're doing, say, a linear amount of time but you're doing it a linear number of times and so it becomes quadratic, and you'll see other polynomial kinds of algorithms.
我们看过一些平方算法，他们一般进行了多次嵌套循环,或者递归迭代调用，对一个线性操作调用线性次,这样就变成平方次了,以后你们能看到,一些多项式算法。
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Typical characterization, not all the time, but typical characterization, is an algorithm that reduces the size of a problem by one, or by some constant amount each time, is typically an example of a linear algorithm.
我们学习过了线性算法，它的典型特征，不是通用的,但是比较典型的特征是，它是逐一减小问题的大小的，或者说是每次减小常数的大小。
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It's not true, by the way, of all programming languages. In fact, Professor Guttag already talked about that, in some languages lists take a time linear with the length to get to it.
顺便说一句这在大部分，编程语言中做不到，实际上Guttag教授已经说过这一点了，在一些语言中取得数组,要花费时间是线性长度的。
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