http://acm.hdu.edu.cn/showproblem.php?pid=6390 题意:求一个式子 题解:看题解,写代码 第一行就看不出来,后面的sigma公式也不会化简.mobius也不会 就自己写了个容斥搞一下(才能维持现在的生活) //别人的题解https://blog.csdn.net/luyehao1/article/details/81672837 #include <iostream> #include <cstdio> #include <cstr…

题意 给一个\(n\),计算 \[\sum_{i=1}^{n}\sum_{j=1}^{i-1}[gcd(i + j, i - j) = 1]\] 题解 令\(a = i - j\) 要求 \[\sum_{i=1}^{n}\sum_{j=1}^{i-1}[gcd(i + j, i - j) = 1]\] 即求 \[\sum_{i=1}^{n}\sum_{a=1}^{i-1}[gcd(2*i - a, a) = 1]\] 根据\(gcd\)的性质,即 \[\sum_{i=1}^{n}\sum_{a=…

Become A Hero Time Limit: 15000/5000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 210    Accepted Submission(s): 57 Problem Description Lemon wants to be a hero since he was a child. Recently he is reading a book…

The Euler function Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 5235    Accepted Submission(s): 2225 Problem Description The Euler function phi is an important kind of function in number theo…

2^x mod n = 1 Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)Total Submission(s): 15810    Accepted Submission(s): 4914 Problem Description Give a number n, find the minimum x(x>0) that satisfies 2^x mod n = 1.   I…

Description has only two Sentences Time Limit: 3000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)Total Submission(s): 1071    Accepted Submission(s): 323 Problem Description an = X*an-1 + Y and Y mod (X-1) = 0.Your task is to cal…

题意: 求出来区间[1,n]内与n互质的数的数量 题解: 典型的欧拉函数应用,具体见这里:Relatives POJ - 2407 欧拉函数 代码: 1 #include<stdio.h> 2 #include<string.h> 3 #include<iostream> 4 #include<algorithm> 5 #include<math.h> 6 using namespace std; 7 typedef long long ll;…

裸题 O(nlogn): #include <cstdio> #include <iostream> #include <algorithm> using namespace std; typedef long long ll; const int maxn=3000000+100; int phi[maxn]; void init() { for(int i=2;i<maxn;i++) phi[i]=i; for(int i=2;i<maxn;i++) i…

题意: 定义函数\(f(n)\)为\(i \cdot j \not\equiv 0 \; (mod \; n)\)的数对\((i,j)\)的个数\((0 \leq i,j \leq n)\) \(g(n)=\sum_{d|n}f(d)\),求\(g(n) \; mod \; 2^{64}\),其中\(1 \leq n \leq 10^9\) 仰慕叉老师手推公式 分析: 计算\(f(n)\) \(f(n)\)不容易计算,但可以计算它的反面,也就是计算满足\(ij \equiv 0 \; (mod…

GCD Again Time Limit: 1000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 2874    Accepted Submission(s): 1240 Problem Description Do you have spent some time to think and try to solve those unsolved problem af…