/in/foo.cc: In function 'int main()':
/in/foo.cc:27:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i < ans.size(); ++i)
                  ~~^~~~~~~~~~~~
/in/foo.cc:38:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i = 0; i < ans.size(); ++i){ 
                  ~~^~~~~~~~~~~~
/in/foo.cc:39:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < ans[i].size(); ++j)
                   ~~^~~~~~~~~~~~~~~