foo.cc: In function 'std::string solve(std::string&, std::string&, std::string&)':
foo.cc:12:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |         while (i < s.size())
      |                ~~^~~~~~~~~~
foo.cc:17:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |                 if (j == t.size()) j = 0, res += u;
      |                     ~~^~~~~~~~~~~

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