foo.cc: In function 'std::string solve(std::string&, std::string&, std::string&)':
foo.cc:10:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |     while (i < s.size())
      |            ~~^~~~~~~~~~
foo.cc:23:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   23 |         if (j == t.size()) res += u, j = 0;
      |             ~~^~~~~~~~~~~

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