/in/foo.cc: In function 'int bfs(int)':
/in/foo.cc:31:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int i = 0; i < child[u.d].size(); ++i)
                   ~~^~~~~~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:52:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < child[0].size(); ++i)
                 ~~^~~~~~~~~~~~~~~~~