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

Solution 1

Python Code
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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

Java Code
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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;
    }
}

C++ Code
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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;
    }
};

Go Code
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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
}