/in/foo.cc: In function 'bool bfs()':
/in/foo.cc:34:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i=0;i<G[u].size();++i){
                ~^~~~~~~~~~~~
/in/foo.cc: In function 'int dfs(int, int)':
/in/foo.cc:48:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int &i=cur[x];i<G[x].size();++i){
                     ~^~~~~~~~~~~~
/in/foo.cc: In function 'bool spfa(int&)':
/in/foo.cc:78:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i=0;i<G[u].size();++i){
                ~^~~~~~~~~~~~