/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:12:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<tr[x].size();i++){
              ~^~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int, int, int)':
/in/foo.cc:22:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<tr[x].size();i++)
              ~^~~~~~~~~~~~~