Perfect Number

Question

We define the Perfect Number is a positive integer that is equal to the sum of all its positive divisors except itself.

Now, given an integer n, write a function that returns true when it is a perfect number and false when it is not. Example:

Input: 28
Output: True
Explanation: 28 = 1 + 2 + 4 + 7 + 14

Note: The input number n will not exceed 100,000,000. (1e8)

Tags

• Mathematics

Thought

Loop to find all divisor and sum them together.

Code

class Solution(object):
    def checkPerfectNumber(self, num):
        """
        :type num: int
        :rtype: bool
        """
        total, div = 1, 2
        while div**2 <= num:
            if num % div == 0:
                total += div
                if div * div != num:
                    total += num / div
            div += 1
        return num > 1 and total == num