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`