python/TangDou/AcWing/Math/Euler.cpp

#include <bits/stdc++.h>

using namespace std;

/**
 * 功能：欧拉函数 互质的概念理解：gcd(x,y)=1
 * @param x
 * @return
 */
int phi(int x) {
    int res = x;
    for (int i = 2; i <= x / i; i++)
        if (x % i == 0) {
            res = res / i * (i - 1);
            while (x % i == 0) x /= i;
        }
    if (x > 1) res = res / x * (x - 1);
    return res;
}

int main() {
    for (int i = 1; i <= 10; i++)
        cout << "i=" << i << " phi[" << i << "]=" << phi(i) << endl;
    //以9为例，与9形成gcd(x,9)=1的x共有6个，分别是(1,2,4,5,7,8)
    return 0;
}