Leetcode 507 - Perfect number

Note:

  • Remember to get all divisors, just search between [sqrt(n), n].

Question:

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:

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Input: num = 28
Output: true
Explanation: 28 = 1 + 2 + 4 + 7 + 14
1, 2, 4, 7, and 14 are all divisors of 28.

Code:

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/**
* @param {number} num
* @return {boolean}
*/
var checkPerfectNumber = function(num) {
if (num === 1) return false;
let sum = 0;
for (let i = num; i >= Math.ceil(Math.sqrt(num)); i--) {
if (num % i === 0) sum += (i + num / i);
}
return (sum - num) === num;
};