507.cpp

// Osqrt-3ms.cpp
class Solution {
public:
  bool checkPerfectNumber(int num) {
    if (num == 1)
      return 0;
    int sum = 1, i;
    for (i = 2; i * i < num; ++i) {
      if (num % i == 0) {
        sum += i;
        sum += num / i;
      }
    }
    if (i * i == num)
      sum += i;
    return sum == num;
  }
};