题解 | 完全数计算

#include <iostream>
#include <set>
using namespace std;

bool is_perfect(int n) {
    if(n < 6) return false;
    set<int> factor;
    for(int i = 1; i <= n / 2; ++i) {
        if(n % i == 0) factor.insert(i);
    }
    int sum = 0;
    for(const int& n: factor) {
        sum += n;
    }
    return sum == n;
}

int main() {
    int n;
    cin >> n;
    int ans = 0;
    for(int i = 6; i <= n; ++i) {
        if(is_perfect(i)) ++ans;      
    }
    cout << ans << endl;
    return 0;
}