/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:17:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |         for (int j = 0; j < a[x].size(); j ++) {
      |                         ~~^~~~~~~~~~~~~