foo.cc: In function 'void Solve()':
foo.cc:18:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   18 |         for(int i=0; i<str.size(); i++)
      |                      ~^~~~~~~~~~~

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