common_prefix

template <typename Container>
auto common_prefix(Container const & strings)
{
    auto const first = std::begin(strings.front());
    auto last = std::end(strings.front());
    auto current_str = std::next(std::begin(strings));
    auto const end_str = std::end(strings);

    while (current_str != end_str) {
        auto [mismatch, _] = std::mismatch(
            first, last,
            current_str->begin(), current_str->end()
        );
        last = mismatch;
        ++current_str;
    }

    return std::string(first, last);
}