/in/foo.cc: In function 'void dfs()':
/in/foo.cc:25:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
      if(len > ans.size())
         ~~~~^~~~~~~~~~~~
/in/foo.cc:28:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
       for(i=0; i<ans.size(); i++)
                ~^~~~~~~~~~~
/in/foo.cc:46:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for(j=0; j<oper[i].size(); j++)
                      ~^~~~~~~~~~~~~~~
/in/foo.cc:58:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if(mem[s] == 0 || ans.size()+1 < mem[s])
                               ~~~~~~~~~~~~~^~~~~~~~
/in/foo.cc:75:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for(j=0; j<oper[i].size(); j++)
                      ~^~~~~~~~~~~~~~~