利用了STL，思路易懂，但是如果舍弃STL实现有点难度

class Solution {
  public:
    string PrintMinNumber(vector<int> numbers) {
      std::string res;
      if (numbers.empty()) {
        return res;
      }
      
      std::sort(numbers.begin(), numbers.end(), [](int a, int b) -> bool {return std::to_string(a) + std::to_string(b) < std::to_string(b) + std::to_string(a);});
      
      for (int i = 0; i < numbers.size(); ++i) {
        res += std::to_string(numbers[i]);
      }
      
      return res;
    }
};