vector<vector<int>> store(26, vector<int>());
  for (int i = 0; i < S.size(); ++i) {
      // 存储字母跟index
      store[S[i] - 'a'].push_back(i);
  }

int numMatchingSubseq(string S, vector<string>& words) {
    vector<vector<int>> store(26, vector<int>());
    for (int i = 0; i < S.size(); ++i) {
        // 存储字母跟index
        store[S[i] - 'a'].push_back(i);
    }

    int res = 0;
    for (auto &word: words) {
        int x = -1;
        bool found = true;
        for (auto c: word) {
            // search
            auto it = upper_bound(store[c - 'a'].begin(), store[c - 'a'].end(), x);
            if (it == store[c - 'a'].end()) {
                found = false;
                break;
            } else {
                // 更新最新的下标位置
                x = *it;
            }
        }
        if (found) res++;
    }

    return res;
}

int numMatchingSubseq(string S, vector<string>& words) {
    vector<pair<int, int>> waiting[128];
    for (int i = 0; i < words.size(); i++)
        waiting[words[i][0]].emplace_back(i, 1);
    for (char c : S) {
        auto advance = waiting[c];
        waiting[c].clear();
        for (auto it : advance)
            waiting[words[it.first][it.second++]].push_back(it);
    }

    return waiting[0].size();
}