foo.cc: In function 'void dfs(int, int)':
foo.cc:27:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(register int i = 0; i < G[u].size(); ++i){
                             ~~^~~~~~~~~~~~~
foo.cc: In function 'void color(int, int)':
foo.cc:52:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(register int i = 0; i < G[u].size(); ++i){
                             ~~^~~~~~~~~~~~~
foo.cc: In function 'bool check(int)':
foo.cc:75:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(register int i = 0; i < G[1].size(); ++i){
                             ~~^~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:109:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if(m < G[1].size()){
        ~~^~~~~~~~~~~~~
foo.cc:116:21: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
         int mid = l + r >> 1;
                   ~~^~~

自豪的采用 HydroJudge 进行评测(github.com/hydro-dev/HydroJudge)

{"receive":"2020-08-09T05:58:43.958Z","handle":"2020-08-09T05:58:43.958Z","cache_start":"2020-08-09T05:58:43.967Z","read_cases":"2020-08-09T05:58:44.079Z","judge":"2020-08-09T05:58:44.084Z","done":"2020-08-09T05:58:48.564Z"}