Question

507. Perfect Number

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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

Solution 1

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

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;
  }
};

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
}