Perfect Number

一个数是Perfect number就是他的factor的和等于这个数. 那么先求factor, 然后求和就可以了.

class Solution {
    public boolean checkPerfectNumber(int num) {
        if(num <= 0)
            return false;
        int sum = 0;
        for(int i = 1; i <= Math.sqrt(num); i++) {
            if(num % i == 0) { // if it is a factor
                sum += i;
                if (i * i != num) { // adding num / i
                    sum += num / i;
                }
            }
        }
        System.out.println(sum);
        return sum - num == num;
    }
}