zipfian分布

zipf law ：在给定的语料中，对于任意一个term，其频度(freq)的排名（rank）和freq的乘积大致是一个常数。

It is known that the number of incoming links to pages on the Web follows a Zipfian distribution. That is, a small number of Web pages have an extremely large number of links pointing to them, while a majority of pages have only a small number of incoming links.

所以：我们可以，找到topk受欢迎的，然后说好了这些url不再交换。