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// @Title: 完美数 (Perfect Number)
// @Author: 15816537946@163.com
// @Date: 2021-12-31 15:49:38
// @Runtime: 0 ms
// @Memory: 5.3 MB

bool checkPerfectNumber(int num) {
  if (num == 1 || num < 0)
    return false;

  int i = 2;
  int res = 1;
  for (; i < sqrt(num); i++) {
    if (num % i == 0)
      res += i + num / i;
  }

  /*
    if ((int(sqrt(num)) >= i) && (num % i == 0))
      res += i;
  */

  return res == num;
}

/*
class Solution {
public:
    bool checkPerfectNumber(int num) {
        if ((num == 1) || (num < 0)) // edge cases - number is negitive or 1
            return false;

        int i = 2;
        int res = 1;
        for (; i<sqrt(num); i++)
        {
            if (num % i == 0)
                res += i + num/i;
        }

        if ((int(sqrt(num)) >= i ) && (num % i == 0)) // edge case - number has
a whole sqrt res += i;

        return res == num;
    }
};

*/