[leetcode-507-Perfect Number]

We define the Perfect Number is a positive integer that is equal to the sum of all its positive divisors except itself.

Now, given an integer n, write a function that returns true when it is a perfect number and false when it is not.

Example:

Input: 28
Output: True
Explanation: 28 = 1 + 2 + 4 + 7 + 14

Note: The input number n will not exceed 100,000,000. (1e8)

 思路：

分解因子即可，注意只需要判断到sqrt(inputNum)即可，否则会超时。

   bool checkPerfectNumber(int num) {
        if (num <= 2) return false;
        
        int sum = 1;
        for (int i = 2; i <=sqrt(num);i++)
        {
            if (num%i == 0)
            {
                sum += i;
                sum += (num / i);
            }
        }
        if (sum == num)
        {
            return true;
        }
        return false;
    }