HDU 4473 Exam 枚举

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原题转化为求a*b*c <=n中选出两个数组成有序对<a,b>的选法数. 令a<=b<=c.... 分情况讨论: (1)全部相等,即a = b = c. 选法有n^(1/3). (2)有两个相等,则设相等的值为i,枚举i = 1到i*i <= n ,剩下的一个数的最大值为t = n/(i*i).当t >=i时,t = i这一种要删除,因为t = i则三个数都相等了,这种选法有3种,所以ans += 3*(t-1).t<i就ans += 3*t; (3)三个数…

hdu 4473 Exam 数学

思路: 将条件转化为满足abc<=n的abc的数目. 1.3个数相等时,为 A; 2.有2个数相等时,为 B; 3.都不相等时,为 C. 则结果为A+3*B+6*C. 代码如下: #include<iostream> #include<stdio.h> #include<algorithm> #include<iomanip> #include<cmath> #include<cstring> #include<vecto…

hdu 2489（枚举 + 最小生成树）

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HUD 4473 Exam

题目地址: http://acm.hdu.edu.cn/showproblem.php?pid=4473 题目意思定义f(x) = 满足(a * b)|x的有序对(a,b)的个数. 然后输入一个n,求f(1) + f(2) + ... + f(n) 废话不多说,此题的关键在于: 把原题的条件(a * b)|x 转化为 a * b * y = x 然后就很好计算了,就是,输入一个n,计算有多少有序对(a, b ,y)满足a*b*y<=n 不妨设a<=b<=y 则,a<=n^(1/3…

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