/in/foo.cc: In function 'void BFS1()':
/in/foo.cc:36:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int k=0;k<g[i].size();k++){
               ~^~~~~~~~~~~~
/in/foo.cc: In function 'void BFS2()':
/in/foo.cc:54:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int k=0;k<gr[i].size();k++){
               ~^~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:76:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int k=0;k<g[i].size();k++){
               ~^~~~~~~~~~~~