/in/foo.cc: In function 'int mex(std::vector<int>&)':
/in/foo.cc:7:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a.size(); i++)
                     ~~^~~~~~~~~~
/in/foo.cc:9:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (a[i] >= 0 && a[i] < a.size())
                                
/in/foo.cc:12:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a.size(); i++)
                     ~~^~~~~~~~~~