题解 | #完全数计算#

#include <stdio.h>
#include <string.h>
#include <math.h>
//参考素数的计算吧,主要是用sqrt n减少循环次数
int is_total_num(int n);
int main()
{ 
    int n;
    int count;
    while (scanf("%d", &n) != EOF)
    {
        count = 0;
        for (int j = 2; j <= n; j++)
        {
            if (is_total_num(j))
                count++;
        }
        printf("%d\n", count);
    }

    return 0;
}

int is_total_num(int n)
{
    int ret = 0;
    for (int i = 2; i <= sqrt(n); i++)
    {
        if (n%i == 0)
        {
            ret += i;
            if (n / i != i)
                ret += n / i;
        }
    }
    //加上因子1
    ret++;
    if (ret != n)
        ret = 0;
    return ret;
}