⑤处应填

（枚举因数）从小到大打印正整数 n 的所有正因数。试补全枚举程序。

#include <bits/stdc++.h>
using namespace std;

int main() {
    int n;
    cin >> n;

    vector<int> fac;
    fac.reserve((int)ceil(sqrt(n)));

    int i;
    for (i = 1; i * i < n; ++i) {
        if (①) {
            fac.push_back(i);
        }
    }

    for (int k = 0; k < fac.size(); ++k) {
        cout << ② << " ";
    }
    if (③) {
        cout << ④ << " ";
    }
    for (int k = fac.size() - 1; k >= 0; --k) {
        cout << ⑤ << " ";
    }
}