cpp



class Solution {
public:
    vector<string> findRepeatedDnaSequences(string s) {
        vector<string> sequences;
        if(s.size()<10) return  sequences;
        unordered_map<string, int> count;

        for (int i = 0; i <= s.length() - 10; i++) {
            string sequence = s.substr(i, 10);
            count[sequence]++;

            if (count[sequence] == 2) {
                sequences.push_back(sequence);
            }
        }

        return sequences;
    }
};