187. Repeated DNA Sequences.java

public class Solution {
    public List<String> findRepeatedDnaSequences(String s) {
        List<String> res = new LinkedList<String>();
        Set<String> explored = new HashSet<String>();
        Set<String> repeat = new HashSet<String>();//avoid repetition in res 
        
        for( int i = 0; i < s.length() - 9; i++){
            String temp = s.substring(i,i + 10);
            if(!explored.add(temp) && repeat.add(temp)){
                res.add(temp);
            }
        }
        return res;
    }
}