leetcode-507-easy

Perfect Number

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

思路一：枚举，遍历 [1, n] 的数

public boolean checkPerfectNumber(int num) {
    int sum = 1;
    int z = num / 2;
    for (int i = 2; i < z; i++) {

        int x = num % i;
        if (x == 0) {
            sum += i;
            z = num / i;
            if (z != x) sum += z;
        }
    }

    return sum == num;
}