/in/foo.cc: In function 'void bfs()':
/in/foo.cc:21:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<son[x].size();i++){
                     ~^~~~~~~~~~~~~~
/in/foo.cc: In function 'void tarjan(int)':
/in/foo.cc:41:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<son[u].size();i++){
                 ~^~~~~~~~~~~~~~
/in/foo.cc:52:13: warning: unused variable 'y' [-Wunused-variable]
         int y;
             ^
/in/foo.cc: In function 'void work()':
/in/foo.cc:65:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0;j<son[i].size();j++){
                     ~^~~~~~~~~~~~~~