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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
    }
    

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