PerfectNumber.java

public class PerfectNumber {

    /*
    Perfect Number
    What is the perfect number?
    A perfect number is a positive integer which is equal
    to the sum of its proper positive divisors.
    Proper positive divisors are positive integers that
    fully divide the perfect number without leaving a remainder
    and exclude the perfect number itself.
    For example, take the number 6:
    Its proper divisors are 1, 2, and 3
    (since 6 is the value of the perfect number, it is excluded),
    and the sum of its
    proper divisors is 1 + 2 + 3 = 6.
    Therefore, 6 is a perfect number
    (as well as the first perfect number).
    Write a method named isPerfectNumber with one parameter
    of type int named number.
    If number is < 1, the method should return false.
    The method must calculate if the number is perfect.
    If the number is perfect, the method should return true;
    otherwise, it should return false.

    HINT: Use a while or for loop.
    HINT: Use the remainder operator.
     */
    public static void main(String[] args) {
        System.out.println(isPerfectNumber(6));
        System.out.println(isPerfectNumber(28));
        System.out.println(isPerfectNumber(5));
        System.out.println(isPerfectNumber(-1));
    }

    public static boolean isPerfectNumber(int number) {
        if (number < 1) {
            return false;
        }
        int sum = 0;

        for (int i = 1; i < number; i++) {
            if (number % i == 0) {
                sum += i;
            }
        }
        return sum == number;
    }
}