187. Repeated DNA Sequences

class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        
       HashSet<String> res=new HashSet<>();
        
       HashSet<String> tempset=new HashSet<>();
        
        int i=0,j=10;
        while(j<=s.length())
        {
            
        String tmp=s.substring(i,j);
        
            if(!tempset.add(tmp))
            {
                res.add(tmp);
            }

        i++;
        j++;
            
        }
        
        return new ArrayList<String>(res);
    }
}