Title description
For a positive integer, if it is equal to the sum of all positive factors except itself, we call it a "perfect number".
Given an integer n, if it is a perfect number, return true, otherwise return false
Example
示例 1：
输入：28
输出：True
解释：28 = 1 + 2 + 4 + 7 + 14
1, 2, 4, 7, 和 14 是 28 的所有正因子。
示例 2：
输入：num = 6
输出：true
示例 3：
输入：num = 496
输出：true
示例 4：
输入：num = 8128
输出：true
示例 5：
输入：num = 2
输出：false
prompt
1 <= num <= 108
Problem solving ideas
The idea of this question is to simply add the factors, but note that the loop variable i cannot reach num, so use i*i<=num to narrow the range
Code
bool checkPerfectNumber(int num){
int count=0;
if(num==1)return false;
for(int i=2;i*i<=num;i++){
if(num%i==0)count+=i+num/i;
}return count+1==num?true:false;
}