Let's assume that v(n) is the largest prime number, that does not exceed n; u(n) is the smallest prime number strictly greater than n. Find . Input The first line contains integer t (1 ≤ t ≤ 500) — the number of testscases. Each of the following t li…

D. On Sum of Fractions Let's assume that v(n) is the largest prime number, that does not exceed n; u(n) is the smallest prime number strictly greater than n. Find . Input The first line contains integer t (1 ≤ t ≤ 500) — the number of testscases. Eac…

题目链接:Codeforces 396B On Sum of Fractions 题解来自:http://blog.csdn.net/keshuai19940722/article/details/20076297 题目大意:给出一个n,ans = ∑(2≤i≤n)1/(v(i)*u(i)), v(i)为不大于i的最大素数,u(i)为大于i的最小素数, 求ans,输出以分式形式. 解题思路:一開始看到这道题1e9,暴力是不可能了,没什么思路,后来在纸上列了几项,突然想到高中时候求等差数列时候用到…

http://codeforces.com/problemset/problem/397/D 题意:v(n) 表示小于等于n的最大素数,u(n)表示比n的大的第一个素数,然后求出: 思路:把分数拆分成两个分数相减,你就会发现规律,等于1/2-1/3+1/3-1/5........,找出v(n)和u(n),答案就出来了. #include <cstdio> #include <cstring> #include <algorithm> #define ll long lo…

题目链接 题目意思: 定义v(n)是不超过n的最大素数, u(n)是大于n的最小素数. 以分数形式"p/q"输出 sigma(i = 2 to n) (1 / (v(i)*u(i))), pq为互质整数且q > 0. 通常会想到这个裂项.公式一写发现约掉了许多. 最终是: 所以:AC 注意乘的过程会爆int. #include <cstdio> #include <cstring> #include <cctype> #include <…

Let's assume that v(n) is the largest prime number, that does not exceed n; u(n) is the smallest prime number strictly greater than n. Find . Input The first line contains integer t (1 ≤ t ≤ 500) — the number of testscases. Each of the following t li…

这次运气比较好,做出两题.本来是冲着第3题可以cdq分治做的,却没想出来,明天再想好了. A. On Number of Decompositions into Multipliers 题意:n个数a1,a2, a3...an求n个数相乘与a1*a2*a3*a4...an相等的排列个数. 分析:首先应该对ai分解质因数,求出所有ai中质因数及个数,枚举排列中每个数包含的质因数个数,例如质因数qi,有ni个,相应的排列中数包含质因数qi个数设为x1,x2,....xn, x1+x2+x3..+xn…

---恢复内容开始--- 1. http://www.spoj.com/problems/KAOS/ 题意:给定n个字符串,统计字符串(s1, s2)的对数,使得s1的字典序比s2的字典序要大,s1反一反(abc->cba,记为s1')比s2'的字典序要小. 做法:先把字符串排序,当我们把s[i]当成题意中的s1的时候,j > i,s[j]是不用管的,那我们只需要用Trie树按序插入s',然后统计答案. #include <cstdio> #include <cstring&…

传送门 Description Vladik and Chloe decided to determine who of them is better at math. Vladik claimed that for any positive integer n he can represent fraction   as a sum of three distinct positive fractions in form . Help Vladik with that, i.e for a g…

Fun With Fractions Time Limit: 1000ms, Special Time Limit:2500ms, Memory Limit:65536KB Total submit users: 152, Accepted users: 32 Problem 12878 : No special judgement Problem description A rational number can be represented as the ratio of two integ…