leetcode187. 重复的dna序列

class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        Set<String> set = new HashSet<>();
        Set<String> res = new HashSet<>();
        for (int i = 0; i <= s.length()-10; i++) {
            String str = s.substring(i,i+10);
            if(!set.add(str)){
                res.add(str);
            }
        }
        return new ArrayList<>(res);
    }
}