507. Perfect Number

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Problem

A perfect number is a positive integer that is equal to the sum of its positive divisors, excluding the number itself. A divisor of an integer x is an integer that can divide x evenly.

Given an integer n, return true if n is a perfect number, otherwise return false.

Example 1:

Input: num = 28
Output: true
Explanation: 28 = 1 + 2 + 4 + 7 + 14
1, 2, 4, 7, and 14 are all divisors of 28.

Example 2:

Input: num = 7
Output: false

Constraints:

• 1 <= num <= 10^8

Code

class Solution {
    public boolean checkPerfectNumber(int num) {
        if(num <= 1) return false;
        
        int res = 1;
        
        for(int i = 2; i * i <= num; i++){
            if(num % i == 0){
                res = res + i + (num / i);
            }
        }
        
        return  num == res;
    }
}