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HDU 2824 The Euler function
The Euler function
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 3789 Accepted Submission(s): 1569
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
线性筛选欧拉函数
#include <cstdio>#include <algorithm>#include <cstring>#include <cmath>#include <iostream>using namespace std;const int N = 3000010;long long phi[N];void solve(){ memset( phi , 0 ,sizeof phi ); phi[1] = 1 ; 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(){ ios::sync_with_stdio(false); solve(); for( int i = 2 ; i < N ; ++i ){ phi[i] += phi[i-1] ; } int a , b ; while( cin >> a >> b ){ cout << phi[b] - phi[ a - 1 ] <<endl; }}
HDU 2824 The Euler function
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