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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

• Java
• C++
• Python
• Go

• 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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