https://oj.leetcode.com/problems/repeated-dna-sequences/

    public List findRepeatedDnaSequences(String s) {
        
        // Assumptions...
        
        List toReturn = new ArrayList<>();
        
        Set seen = new HashSet<>();
        
        for (int i = 0 ; i <= s.length() - 10 ; i ++)
        {
            String sub = s.substring(i, i + 10);
            if (seen.contains(sub))
            {
                toReturn.add(sub);
            }
            else
            {
                seen.add(sub);
            }
        }
        return toReturn;
    }