package Maths;

/**
 * In number theory, a perfect number is a positive integer that is equal to the sum of
 * its positive divisors, excluding the number itself. For instance, 6 has divisors 1, 2 and 3
 * (excluding itself), and 1 + 2 + 3 = 6, so 6 is a perfect number.
 * <p>
 * link:https://en.wikipedia.org/wiki/Perfect_number
 * </p>
 */
public class PerfectNumber {
    public static void main(String[] args) {
        assert isPerfectNumber(6); /* 1 + 2 + 3 == 6 */
        assert !isPerfectNumber(8); /* 1 + 2 + 4 != 8 */
        assert isPerfectNumber(28); /* 1 + 2 + 4 + 7 + 14 == 28 */
    }

    /**
     * Check if {@code number} is perfect number or not
     *
     * @param number the number
     * @return {@code true} if {@code number} is perfect number, otherwise false
     */
    public static boolean isPerfectNumber(int number) {
        int sum = 0;  /* sum of its positive divisors */
        for (int i = 1; i < number; ++i) {
            if (number % i == 0) {
                sum += i;
            }
        }
        return sum == number;
    }
}