传送门： 2018 牛客网暑期 ACM 多样训练营（第五场）A gpa
At the university where she attended, the final score of her is ${\sum{s[i]c[i]} \over \sum{s[i]}}$
Now she can delete at most k courses and she want to know what the highest final score that can get.
Polar bears Menshykov and Uslada from the zoo of St. Petersburg and elephant Horace from the zoo of Kiev got hold of lots of wooden cubes somewhere. They started making cube towers by placing the cubes one on top of the other. They defined multiple towers standing in a line as a wall. A wall can consist of towers of different heights.
Ivan wants to write a letter to his friend. The letter is a string s consisting of lowercase Latin letters.
Unfortunately, when Ivan started writing the letter, he realised that it is very long and writing the whole letter may take extremely long time. So he wants to write the compressed version of string s instead of the string itself.
Arseniy is already grown-up and independent. His mother decided to leave him alone for m days and left on a vacation. She have prepared a lot of food, left some money and washed all Arseniy’s clothes.
A permutation of size n is an array of size n such that each integer from 1 to n occurs exactly once in this array. An inversion in a permutation p is a pair of indices (i, j) such that i > j and a**i < *a**j*. For example, a permutation [4, 1, 3, 2] contains 4 inversions: (2, 1), (3, 1), (4, 1), (4, 3).
Let D(x) be the number of positive divisors of a positive integer x. For example, D(2) = 2 (2 is divisible by 1 and 2), D(6) = 4 (6 is divisible by 1, 2, 3 and 6).
Little Mishka enjoys programming. Since her birthday has just passed, her friends decided to present her with array of non-negative integers a1, a2, …, an of n elements!
最近训练时敲代码总爱在 if 语句中有位算符时踩坑， 比如 if(i&1==0) 或 if(i&i-1 == 0)，本意是想判 i 是否为偶数和 i 是否为 2 的幂，但这么写都是错误的，导致程序不能输出正确结果。每次 debug 时又不明所以，耗了很长时间才找到。在这里记录下。
错误的原因是 == 运算符优先级要高于 & | ^ 这三个位运算符，故导致上面代码的判断顺序实际为 if(i & (1==0)) 和 if(i & (i-1 == 0))。 很痛苦呀，有没有。
建议：