20220531 Mathematics: Happy numbers

         Title Description ： Write an algorithm to judge a number n Is it a happy number .

         Happiness number is defined as ： For a positive integer , Replace the number with the sum of the squares of the numbers in each of its positions . Then repeat the process until the number becomes 1, It could be Infinite loop But it doesn't change 1. If this process The result is  1, So this number is the happy number .
         If n yes Happy number Just go back to true ; No , Then return to false .

        coded ：

    public static boolean isHappy(int n) {

        if (n == 1) {
            return true;
        } else {
            Set<Integer> set = new HashSet<>();
            while (n != 1) {
                int temp = n, sum = 0;
                while (temp >= 10) {
                    int mod = temp % 10;
                    temp /= 10;
                    sum += mod * mod;
                }
                sum += temp * temp;
                if (!set.add(sum)) {
                    return false;
                }
                n = sum;
            }
        }
        return true;
    }