/in/foo.cc: In function 'void spfa1()':
/in/foo.cc:14:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(j=0;j<a[i].size();j++){
                 ~^~~~~~~~~~~~
/in/foo.cc: In function 'void spfa2()':
/in/foo.cc:31:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for( j=0;j<b[i].size();j++){
                  ~^~~~~~~~~~~~