507. Perfect Number.java

/**
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)

**/

class Solution {
    public boolean checkPerfectNumber(int num) {
       if (num <= 0) {
            return false;
        }
        int sum = 0;
        for (int i = 1; i * i <= num; i++) {
            if (num % i == 0) {
                sum += i;
                if (i * i != num) {
                    sum += num / i;
                }

            }
        }
        return sum - num == num;
    
    }
}