foo.cc: In function 'void tidy(std::string&)':
foo.cc:27:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   27 |     for (int i = 0; i < str.length(); i++)
      |                     ~~^~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:44:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   44 |     for (int i = 0; i < s.length() - 1; i++)
      |                     ~~^~~~~~~~~~~~~~~~
foo.cc:56:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   56 |     for (int i = 0; i < ans.size(); i++)
      |                     ~~^~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务