/in/foo.cc: In function 'void SPFA(int)':
/in/foo.cc:19:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int k=0;k<to[i].size();k++){
               ~^~~~~~~~~~~~~
/in/foo.cc: In function 'void DFS(int)':
/in/foo.cc:35:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int k=0;k<from[i].size();k++){
              ~^~~~~~~~~~~~~~~