/in/foo.cc: In function 'int main()':
/in/foo.cc:72:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int j=0;j<ans[i].size();j++)
                          ~^~~~~~~~~~~~~~
/in/foo.cc:64:20: warning: 'root' may be used uninitialized in this function [-Wmaybe-uninitialized]
         dfs(root,0);
                    ^