hdu-2824 The Euler function(欧拉函数) The Euler function
题目链接：
Time Limit: 2000/1000 MS (Java/Others)
Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 4987 Accepted Submission(s): 2098
Problem Description
The Euler function phi is an important kind of function in number theory, (n) represents the amount of the numbers which are smaller than n and coprime to n, and this function has a lot of beautiful characteristics. Here comes a very easy question: suppose you are given a, b, try to calculate (a)+ (a+1)+....+ (b)
Input
There are several test cases. Each line has two integers a, b (2<a<b<3000000).
Output
Output the result of (a)+ (a+1)+....+ (b)
Sample Input
3 100
Sample Output
3042
题意：求[a,b]的欧拉函数和;
AC代码：
#include <iostream> #include <cstring> #include <cstdio> #include <algorithm> using namespace std; const int N=3e6+3; int phi[N]; int get_phi() { for(int i=2;i<N;i++) { if(!phi[i]) { for(int j=i;j<N;j+=i) { if(!phi[j])phi[j]=j; phi[j]=phi[j]/i*(i-1); } } } } int main() { get_phi(); int a,b; while(scanf("%d%d",&a,&b)!=EOF) { long long ans=0; for(int i=a;i<=b;i++) { ans+=(long long)phi[i]; } cout<<ans<<" "; } return 0; }