zyq_19960204的博客

DescriptionThis is a small but ancient game. You are supposed to write down the numbers 1, 2, 3, . . . , 2n - 1, 2n consecutively in clockwise order on the ground to form a circle, and then, to dr

Problem DescriptionGiven 5 integers: a, b, c, d, k, you're to find x in a...b, y in c...d that GCD(x, y) = k. GCD(x, y) means the greatest common divisor of x and y. Since the number of choices ma

题目描述给定整数N，求1数对(x,y)有多少对.输入一个整数N输出如题样例输入4样例输出4 解题思路： 这个题目出来可以用欧拉函数来解答之外，点击此处 这是欧拉函数解这道题的思路 那么我们还可以用莫比乌斯反演来做，首先介绍一下莫比乌斯反演的公式： F(n)=∑d|nf(d) ⇒f(n)=∑d|nF(