507. Perfect Number（LeetCode）

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)

 1 class Solution {
 2 public:
 3     bool checkPerfectNumber(int num) {
 4        int sum = 0;
 5         if(num==0)
 6             return false;
 7         for (int i = 1; i*i < num; i++)
 8         {
 9             if (num%i == 0)
10             {
11                 sum += i;
12                 sum += num / i;
13             }
14         }
15         if (sum== num*2)
16             return true;
17         else
18             return false;
19     }
20 };