507. 完全数 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)

static public bool CheckPerfectNumber(int num) {
	if (num == 0 || num == 1) return false;
	int sum = 1;
	for (int i = 2; i < Math.Sqrt(num); i++) {
		if (num % i == 0) {
			sum += i + num / i;
		}
	}
	return sum == num;
}

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