List<bool>? dfsIterative(int v) {
    v--;
    List<bool> label = <bool>[];
    for (int i = 0; i < _amount; i++) {
      label.add(false);
    }
    List<int> stack = <int>[];
    stack.add(v);
    while (stack.isNotEmpty) {
      v = stack.removeLast();
      if (!label[v]) {
        label[v] = true;
        for (int i in _dots[v].getL().keys) {
          stack.add(i - 1);
        }
      }
    }
    return label;
  }