507. Perfect Number

Posted 2022-08-03 wx62ea2466cca9a

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)

public class Solution   
    public boolean checkPerfectNumber(int num)   
        if (num == 1)   
            return false;  
          
        int sum = 1, sqrt = (int)Math.sqrt(num);  
        for (int i = 2; i <= sqrt; i ++)   
            if (num % i == 0)   
                sum += i + (i * i == num? 0: num / i);  
              
          
        return sum == num;