/in/foo.cc: In function 'int spfa()':
/in/foo.cc:41:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<vec[cur].size();i++)
               ~^~~~~~~~~~~~~~~~
/in/foo.cc:57:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^