# 507. Perfect Number

## Description

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

## Solutions

• class Solution {
public boolean checkPerfectNumber(int num) {
if (num == 1) {
return false;
}
int s = 1;
for (int i = 2; i * i <= num; ++i) {
if (num % i == 0) {
s += i;
if (i != num / i) {
s += num / i;
}
}
}
return s == num;
}
}

• class Solution {
public:
bool checkPerfectNumber(int num) {
if (num == 1) return false;
int s = 1;
for (int i = 2; i * i <= num; ++i) {
if (num % i == 0) {
s += i;
if (i != num / i) s += num / i;
}
}
return s == num;
}
};

• class Solution:
def checkPerfectNumber(self, num: int) -> bool:
if num == 1:
return False
s, i = 1, 2
while i * i <= num:
if num % i == 0:
s += i
if i != num // i:
s += num // i
i += 1
return s == num


• func checkPerfectNumber(num int) bool {
if num == 1 {
return false
}
s := 1
for i := 2; i*i <= num; i++ {
if num%i == 0 {
s += i
if i != num/i {
s += num / i
}
}
}
return s == num
}