Write an algorithm to determine if a number is “happy”.

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 19 is a happy number

• 1² + 9² = 82
• 8² + 2² = 68
• 6² + 8² = 100
• 1² + 0² + 0² = 1

class Solution {
    public boolean isHappy(int n) {
        HashSet set = new HashSet();
        int re;
        while(set.add(n)){
            int sum =0;
            while(n>0){
                re = n%10;
                sum += re * re;
                n /= 10;
            }
            if(sum ==1) return true;
            n = sum;
        }
        return n==1;
    }
}