507. Perfect Number

📋 Đề Bài

A perfect number is a positive integer that is equal to the sum of its positive divisors, excluding the number itself. A divisor of an integer x is an integer that can divide x evenly.

Given an integer n, return true if n is a perfect number, otherwise return false.

Example 1:

Input: num = 28
Output: true
Explanation: 28 = 1 + 2 + 4 + 7 + 14
1, 2, 4, 7, and 14 are all divisors of 28.

Example 2:

Input: num = 7
Output: false

Constraints:

1 <= num <= 10⁸

💻 Lời Giải

C++ 0507-perfect-number.cpp

class Solution {
public:
    bool checkPerfectNumber(int num) {
        int sum = 0;
        for (int i = 1; i < num; ++i) {
            if (num % i == 0) {
                sum += i;
                if (sum > num) {
                    return false;
                }
            }
        }
        return sum == num;
    }
};