07/08 [hash]Happy Number

/* Time:O(); Space:O() Logic: 1. perform calculation of a^2 ++ b^2 2. record the value of a^2 ++ b^2 in the HashSet */

public class Solution {
    public boolean isHappy(int n) {
        HashSet set = new HashSet();
        while (!set.contains(n))
        {
            set.add(n);
            n = sum(getDigits(n));
            if ( n ==1 )
            {
                return true;
            }
        }
        return false;
    }
    
    private int sum (int[] arr)
    {
        int sum = 0;
        for ( int i: arr)
        {
            sum+= i*i;
        }
        return sum;
    }
    
    private int[] getDigits(int n)
    {
        String s = String.valueOf(n);
        int[] result = new int[s.length()];
        int i = 0;
        while ( n > 0 )
        {
            int m = n%10;
            result[i++] = m;
            n = n/10;
        }
        return result;
    }
}