507 Perfect Number

A positive integer is called a "perfect number" if it is equal to the sum of all positive factors except itself.
Given a positive integer n, if it is a perfect number, return True, otherwise return False
Example:
Input: 28
Output: True
Explanation: 28 = 1 + 2 + 4 + 7 + 14
Note:
The input number n will not exceed 100,000,000 . (1e8)
See: https://leetcode.com/problems/perfect-number/description/

C++：

class Solution {
public:
    bool checkPerfectNumber(int num) {
        if(num==1)
        {
            return false;
        }
        int sum=1;
        for(int i=2;i*i<=num;++i)
        {
            if(num%i==0)
            {
                sum+=(i+num/i);
            }
            if(i*i==num)
            {
                sum-=i;
            }
            if(sum>num)
            {
                return false;
            }
        }
        return sum==num;
    }
};

 Reference: http://www.cnblogs.com/grandyang/p/6636879.html