题解 | #完全数计算#--遍历找出除其本身的所有因子

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num = in.nextInt();
        int count = 0;
        if (num < 4) {
            System.out.println(count);
        } else {
            // 判断是否是完美数
            for (int i = 4; i <= num; i++) {
                if (isPerfectNum(i)) {
                    count++;
                }
            }
            System.out.println(count);
        }
    }

    private static boolean isPerfectNum(int num) {
        List<Integer> factors = new ArrayList<>();
        // 找出除其本身的所有因子
        for (int i = 1; i <= num / 2; i++) {
            if (num % i == 0) {
                factors.add(i);
            }
        }
        int sum = factors.stream().reduce(Integer :: sum).get();
        if (sum == num) {
            return true;
        }
        return false;
    }
}