you are given a server log file containing billions of lines. Each line
contains a number of fields. For this problem the relevant field is a string
denoting the page that was accessed.
Write a function to read a log file line with O(1) time complexity, and a
function to find the k most visited pages with O(k) time complexity.
想不出来怎么可以用这么少的时间做到
呼唤大牛
