Time: 2020.2.23-2020.2.29
Time spent learning (including classes): an average of 7-8 hours a day
The amount of code: line about 500+
Knowledge learned: The Fenwick tree, such as poj1990 and hdu3015 like these two questions, first sort the array and then use the tree count is smaller than the number of the number of numbers, as well as their and then get an answer.