/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:17:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0, to; i < v[x].size(); i++) {
                     ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int, int)':
/in/foo.cc:27:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0, to; i < v[x].size(); i++) 
                     ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'void print(int*)':
/in/foo.cc:57:2: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
  for(int i = 1; i <= N; i++) printf("%d ", a[i]); puts("");
  ^~~
/in/foo.cc:57:51: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
  for(int i = 1; i <= N; i++) printf("%d ", a[i]); puts("");
                                                   ^~~~