判断一个数是不是快乐数

public static void main(String[] args) {
        /**
         * 示例：
         *
         * 输入：19
         * 输出：true
         * 解释：
         * 1^2 + 9^2 = 82
         * 8^2 + 2^2 = 68
         * 6^2 + 8^2 = 100
         * 1^2 + 0^2 + 0^2 = 1
         *
         * #思路
         */
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        Set<Integer> set = new HashSet<>();
        while (!set.contains(num)){
            set.add(num);
            num = getNum(num);
        }
        System.out.println(num==1);
    }

    private static int getNum(int num) {
        int res = 0;
        while (num > 0){
            int k = num % 10;
            res += k * k;
            num = num / 10;
        }
        return res;
    }