VALUE& operator[](const KEY& key) {
    size_t index = _hash(key) % _table.size();
    LIST& list = _table[index];

    for (auto iter = list.begin(); iter != list.end(); ++iter) {
        if (iter->first == key) {
            return iter->second;
        }
    }

    _size++;
    if (double(_size) / _table.size() > max_coef) {
        this->rehash(_table.size() * size_t(max_coef));

        LIST& new_list = _table[_hash(key) % _table.size()];
        new_list.push_back(PAIR(key, VALUE()));
        return new_list.back().second;
    }

    list.push_back(PAIR(key, VALUE()));

    return list.back().second;
}