foo.cc: In function 'bool check()':
foo.cc:23:20: 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=0; i<s.length(); i++) {
      |                   ~^~~~~~~~~~~
foo.cc:39:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   39 |     for (int i=0; i<t.length(); i++) {
      |                   ~^~~~~~~~~~~
foo.cc: In function 'bool solve()':
foo.cc:48:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   48 |     for (int i=0; i<t.size(); i++) {
      |                   ~^~~~~~~~~
foo.cc:51:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   51 |         if(k==_map[t[i]].size()) return 0;
      |            ~^~~~~~~~~~~~~~~~~~~

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