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 = 6 Output: true Example 3:
Input: num = 496 Output: true Example 4:
Input: num = 8128 Output: true Example 5:
Input: num = 2 Output: false
Constraints:
1 <= num <= 108
public class Solution {
public bool CheckPerfectNumber(int num) {
if(num<2){
return false;
}
int sum = 1;
for(int i=2;i*i<=num;i++){
if(num%i==0){
sum+=i;
sum+=num/i;
}
}
return sum==num;
}
}Time Complexity: O(n)
Space Complexity: O(1)
