左旋一个字符串和手摇反转法

void leftRoutate(std::string& s, size_t offset)
{
    auto reverse = [&](size_t begin, size_t end)
    {
        --end;
        while (begin <= end){
            std::swap(s[begin], s[end]);
            ++begin;
            --end;
        }
    };
    reverse(0, offset);
    reverse(offset, s.length ());
    reverse(0, s.length ());
}