string simplifyPath(string const& path)

      {

          vector<string> dirs;

          for (auto i = path.begin(); i != path.end();)

          {

              i++;

              auto j = find(i, path.end(), '/');

              auto dir = string(i, j);//注意用法

              if (!dir.empty() && dir != ".")//当有连续的///时dir为空

              {

                  if (dir == "..")

                  {

                      if (!dirs.empty())

                          dirs.pop_back();

                  }

                  else

                      dirs.push_back(dir);

              }

              i = j;

          }

          stringstream out;

          if (dirs.empty())

          {

              out << "/";

          }

          else

          {

              for (auto dir : dirs)

              {

                  out << '/' << dir;

              }

          }

          return out.str();

      }