JavaScript-Assignments/js-built-ins/problems/medium/isPerfectNumber.js at a78c86d346d4a16446b94603588def0eb6b12548 · 100xdevs-bootcamp-1/JavaScript-Assignments · GitHub

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/*
  Write a function `isPerfectNumber` which takes an integer `num` as input and returns a boolean indicating whether the number is a perfect number.

  What is a perfect number?
  - A perfect number is a positive integer that is equal to the sum of its proper divisors, excluding the number itself.

  Example:
  - Input: 6
  - Output: true
    - Explanation: The divisors of 6 are 1, 2, and 3. 1 + 2 + 3 = 6, so 6 is a perfect number.

  - Input: 28
  - Output: true
    - Explanation: The divisors of 28 are 1, 2, 4, 7, and 14. 1 + 2 + 4 + 7 + 14 = 28, so 28 is a perfect number.

  - Input: 10
  - Output: false
    - Explanation: The divisors of 10 are 1, 2, and 5. 1 + 2 + 5 = 8, which is not equal to 10, so 10 is not a perfect number.

  - Input: 1
  - Output: false
    - Explanation: The divisors of 1 are none (it doesn't have proper divisors), so 1 is not a perfect number.

  Once you've implemented the logic, test your code by running
  - `npm run test-perfect`
*/

function isPerfectNumber(num) {
  if (num <= 1) return false;

  let summ = 0;

  for (let i = 1; i * i <= num; i++) {

    if (num % i === 0) {

      if (i !== num) {
        summ += i;
      }

      let other = num / i;

      if (other !== i && other !== num) {
        summ += other;
      }
    }
  }

  return summ === num;
}

module.exports = { isPerfectNumber };