AcWing 874. 筛法求欧拉函数( java 实现 )
原题链接
简单
作者:
nighoc
,
2023-03-22 21:19:58
,
所有人可见
,
阅读 77
import java.util.Scanner;
public class Main {
final int N = 1000010;
int[] primes = new int[N];
int[] phi = new int[N];
boolean[] st = new boolean[N];
int cnt = 0;
void get_ora(int x) {
phi[1] = 1;
for (int i = 2; i <= x; i++) {
if(!st[i]) {
primes[cnt++] = i;
phi[i] = i - 1;
}
for (int j = 0; primes[j] <= x / i; j++) {
int t = primes[j] * i;
st[t] = true;
if(i % primes[j] == 0) {
phi[t] = phi[i] * primes[j];
break;
}
phi[t] = phi[i] * (primes[j] - 1);
}
}
}
public Main() {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
scanner.close();
get_ora(n);
long sum = 0;
for (int i = 0; i <= n; i++) {
sum += phi[i];
}
System.out.println(sum);
}
public static void main(String[] args) {
new Main();
}
}