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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:
Input: 28
Output: True
Explanation: 28 = 1 + 2 + 4 + 7 + 14
- Note: The input number n will not exceed 100,000,000. (1e8)
题意：计算整数N是否为Perfect Number，其定义为满足其所有因数（不包括自身）的和与该数相等；
解法：只需要计算其所有因数并求和后与此数相比较即可，这里需要注意的是给出的整数N可能为负数或零，而Perfect Number要求是正整数；
Java
class Solution {
public boolean checkPerfectNumber(int num) {
int sum = 0;
for (int i = 1; i <= num / 2; i++) {
if (num % i == 0) sum += i;
}
return num <= 0 || num != sum ? false : true;
}
}