欧拉函数与原根

#include <cstdio>
#include <cstring>
#include <vector>

using namespace std;
//奇素数的原根个数=phi(phi(n))=phi(n-1);
//大佬的代码
const int kMax = 100000 + 10;

int n;
int num[kMax];
vector<int> table;

void build() {
    memset(num, true, sizeof(num));
    num[0] = num[1] = false;
    for(int i = 2;i < kMax;++ i) {
        if(num[i]) {
            table.push_back(i);
            for(int j = i + i;j < kMax;j += i) num[j] = false;
        }
    }
}

int main() {
    build();
    while(scanf("%d", &n) != EOF) {
        -- n;
        int res = n;
        for(int i = 0;i < table.size() && table[i] <= n;++ i) {
            if(n % table[i] == 0) {
                res = res / table[i] * (table[i] - 1);
            }
        }
        printf("%d\n", res);
    }
}