/in/foo.cc: In function 'void SPFA1(int)':
/in/foo.cc:18:16: 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 SPFA2(int)':
/in/foo.cc:42:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int k=0;k<from[i].size();k++){
               ~^~~~~~~~~~~~~~~