Leetcode507-perfectNumber

Description

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

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

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

Solution

class Solution {
    public boolean checkPerfectNumber(int num) {
        if (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);
    }
}