题解 | #完全数计算#

#include <iostream>
#include <cmath>
#include <vector>
using namespace std;

bool perfectNumber(int m)
{
    if(m==1)
        return false;
    vector<int> divisors;
    divisors.push_back(1);
    int l = sqrt(m);
    for(int i = 2;i<=l;++i)
    {
        if(m%i==0)
        {
            divisors.push_back(i);
            int t = m/i;
            if(t!=i)
                divisors.push_back(t);
        }
    }
    l=0;
    for(auto &i:divisors)
    {
        l+=i;
    }
    if(l==m)
        return true;
    return false;
}

int howManyPerfectNumber(int n)
{
    int count = 0;
    for(int i = 1;i!=n+1;i++)
    {
        if(perfectNumber(i))
            ++count;
    }
    return count;
}

int main() {
    int n;
    cin>>n;
    cout<<howManyPerfectNumber(n);
}
// 64 位输出请用 printf("%lld")