List<int?> dijkstra(int from) {
    List<int?> d = List<int?>.filled(_amount, intMax);
    List<int> p = List<int>.filled(_amount, -1);

    d[from - 1] = 0;
    List<bool> u = List<bool>.filled(_amount, false);
    for (int i = 0; i < _amount; ++i) {
      int v = -1;
      for (int j = 0; j < _amount; ++j) {
        if (!u[j] && (v == -1 || d[j]! < d[v]!)) {
          v = j;
        }
      }
      if (d[v] == intMax) break;
      u[v] = true;
      for (int to in _dots[v].getL().keys) {
        int len = _dots[v].getL()[to]!;
        if (!_useLength && len == 0) len = 1;
        if (d[v]! + len < d[to - 1]!) {
          d[to - 1] = d[v]! + len;
          p[to - 1] = v;
        }
      }
    }
    for (int i = 0; i < d.length; i++) {
      if (d[i] == intMax) d[i] = null;
    }
    return d;
  }