/in/foo.cc: In function 'void dfs1(int, int)':
/in/foo.cc:14:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < adj[u].size(); ++i) {
                   ~~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int, int)':
/in/foo.cc:30:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < adj[u].size(); ++i) {
                   ~~^~~~~~~~~~~~~~~