[模板] 线筛欧拉函数

今天复习了一些数学方面的东西，线性筛欧拉是个很重要的东西，先贴代码，免得以后又忘了。

#include <iostream>
#include <cstdlib>
typedef long long LL;

int phi[(int)1e7], p[(int)1e7];
int t;

void Phi(int n) {
    for (int i = 2; i <= n; i++) {
        if(!phi[i]) phi[p[t++] = i] = i - 1;
        for (int j = 0; j < t && (LL)i * p[j] <= n; j++) {
            if(i % p[j] == 0) {phi[i * p[j]] = phi[i] * p[j]; break;}
            phi[i * p[j]] = phi[i] * (p[j] - 1);
        }
    }
}

int main() {
    int n;
    std::cin >> n;
    Phi(n);
    for (int i = 1; i <= n; i++) std::cout << phi[i] << ' ';
    system("pause");
    return 0;
}

转载于:https://www.cnblogs.com/ZegWe/p/6048893.html