foo.cc: In function 'void spfa()':
foo.cc:18:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<E[u].size();++i){
               ~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:32:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    scanf("%d %d %d",&u,&v,&w);
    ~~~~~^~~~~~~~~~~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。