/in/foo.cc: In function 'void DFS(int, int)':
/in/foo.cc:24:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 #define rep(i,a,b) for(int i = (a);i < (b);i++)
                                      ^
/in/foo.cc:41:2: note: in expansion of macro 'rep'
  rep(i, 0, to[pos].size()){
  ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:54:9: warning: unused variable 'M' [-Wunused-variable]
  int N, M, T, i, j, k;
         ^
/in/foo.cc:54:12: warning: unused variable 'T' [-Wunused-variable]
  int N, M, T, i, j, k;
            ^
/in/foo.cc:54:15: warning: unused variable 'i' [-Wunused-variable]
  int N, M, T, i, j, k;
               ^
/in/foo.cc:54:18: warning: unused variable 'j' [-Wunused-variable]
  int N, M, T, i, j, k;
                  ^
/in/foo.cc:54:21: warning: unused variable 'k' [-Wunused-variable]
  int N, M, T, i, j, k;
                     ^