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)
没啥好说的，直接求因子求和

class Solution {
public:
    bool checkPerfectNumber(int num) {
        vector<int> v;
        if (num == 1) return false; 
        v.push_back(1);
        for (int i = 2; i * i < num; ++i) {
            if (num % i == 0) {
                v.push_back(i);
                v.push_back(num / i);
            }
        }
        return (accumulate(v.begin(), v.end(), 0) == num);
    }
};