Happy number -- Leetcode

Question:

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

Answer:
Note using HashSet to avoid endless loop!
public class Solution {
    public boolean isHappy(int n) {
        HashSet<Integer> set = new HashSet<Integer>();
       
        int res = Util(n);
        while(res!=1){
            if(set.contains(res)==false){
                set.add(res);
            }else{
                break;
            }
            res = Util(res);
        }
        if(res == 1){
            return true;
        }
        return false;
    }
   
    int Util(int n){
        ArrayList<Integer> numbers = new ArrayList<Integer>();
        int p= n/10;
        int q= n%10;
        numbers.add(q);
        while(p>0){
            q= p%10;
            p= p/10;
            numbers.add(q);
        }
        int res = computeRes(numbers);
        return res;
    }
    int computeRes(ArrayList<Integer> numbers){
        int res=0;
        for(int i=0; i<numbers.size(); ++i){
            res += numbers.get(i) * numbers.get(i);
        }
        return res;
    }
}