Python中“ set.intersection()”的算法是什么? [英] What's the algorithm of 'set.intersection()' in python?
问题描述
首先,我的目的是随机获得两个已知集中的一个元素。所以我的原始方法是首先将两个集合相交。然后从相交的集合中随机选取一个元素。但这是愚蠢的,因为我只需要一个元素,但需要一个相交的集合。
First of all, my purpose is to randomly get only one element in both known sets. So my original method is firstly intersect two sets. And then randomly pick up a element from the intersected set. But this is foolish, because that I only need a elements but a intersected set.
所以我需要找到set.intersection()的算法。
So I need to find the algorithm of set.intersection().
我比较了 set.intersection()和 for {for {}}的方法。 Set.intersection()比其他方法快100倍。因此,使用 for {for {}}来随机选择元素不是一个明智的主意。
I compare the cost time between the methods of 'set.intersection()' and 'for{for{}}'. Set.intersection() is more faster than other one(100 times). So using 'for{for{}}' to pick up a randomly elements is not a wise idea.
python set.intersection()背后的算法是什么?
What's the algorithm behind set.intersection() in python?
推荐答案
算法如下:较小的集合被循环遍历,并且根据是否在较大的集合中找到每个元素,将其复制。因此,它等于C的
The algorithm is as follows: the smaller set is looped over and every element is copied depending whether it's found in the bigger set. So, it's the C equivalent of
def intersect(a, b):
if len(a) > len(b):
a, b = b, a
c = set()
for x in a:
if x in b:
c.add(x)
return c
(或: return set(x表示x如果a中的x表示x)
。)
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