foo.cc: In function 'int a(std::string)':
foo.cc:7:25: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    7 |         for(int i = 0;i < s.length(); i++)
      |                       ~~^~~~~~~~~~~~
foo.cc:11:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |             for(int j = i; j < s.length(); j++)
      |                            ~~^~~~~~~~~~~~
foo.cc:13:32: warning: array subscript has type 'char' [-Wchar-subscripts]
   13 |                 if(visited[s[j]] != 0)
      |                                ^
foo.cc:16:29: warning: array subscript has type 'char' [-Wchar-subscripts]
   16 |                 visited[s[j]]++;
      |                             ^

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