docs: public int nextIndex(int weight) {
      if(used == parent.length) {
        int nsize = used + (used >> 1);
        this.weight = Arrays.copyOf(this.weight, nsize);
        this.parent = Arrays.copyOf(this.parent, nsize);
      }
      this.weight[used] = weight;
      this.parent[used] = used;
      return used++;
    }