findRepeatedDNASequence.cpp

//Since DNA sequence only consists ACTG, which can be distinguished by the ending 3bits, that is a sequence of 10 letters can be represent as a binary of 30 bits.
vector<string> findRepeatedDnaSequences(string s) {
    unordered_map<int, int> m;
    vector<string> r;
    for (int t = 0, i = 0; i < s.size(); i++)
        if (m[t = t << 3 & 0x3FFFFFFF | s[i] & 7]++ == 1)
            r.push_back(s.substr(i - 9, 10));
    return r;
}