foo.cc: In function 'bool check(std::string&, int)':
foo.cc:23:34: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   23 |     for (int i = s.size() - k; i < s.size(); ++i) {
      |                                ~~^~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:43:27: warning: comparison of integer expressions of different signedness: 'int' and 'long long unsigned int' [-Wsign-compare]
   43 |         for (int i = 0; i <= str.size() - k; ++i) {
      |                         ~~^~~~~~~~~~~~~~~~~

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