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
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Note: The input number n will not exceed 100,000,000. (1e8)
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| public class Solution {
public boolean checkPerfectNumber(int num) {
if (num < 2) return false;
int sqrt = (int) Math.sqrt(num);
int result = 1;
for (int i = 2; i <= sqrt; i++) {
if (num % i == 0) {
result += i + (num / i);
}
}
if (sqrt * sqrt == num) {
result -= sqrt;
}
return result == num;
}
}
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