/in/foo.cc: In function 'void dfs1(int, int, int)':
/in/foo.cc:14:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < G[x].size(); i++) {
                     ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int, int)':
/in/foo.cc:25:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < G[x].size(); i++) {
                     ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'void modify_col(int, int)':
/in/foo.cc:122:73: warning: 'tmp' may be used uninitialized in this function [-Wmaybe-uninitialized]
             pl = tid[r], pr = tid[r] + sz[r] - 1, v = fa[r], col_top[t] = tmp;
                                                              ~~~~~~~~~~~^~~~~