LeetCode 507---Perfect Number

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)

解决方案(Java):

public class Solution {
public static boolean checkPerfectNumber(int num) {
if(num == 1 || num >= 100000000) return false;
int res = 1;
int last = num;
for(int i = 2; i < last; i++) {
if(num % i == 0 ) {
last = num / i;
res = res + i + num / i;
}
}
return res == num;
}
}

可能出现的错误：

1. 1和100000000的判断；

2. 复杂度的判断（报错：

Time Limit Exceed

）。