message: fine tuning Vector
diff: class Vector<T> {
  private map: Map<number, T> = new Map();
  - private maxId: number = 0;
  + private maxId_: number = 0;
  public set(id: number, value: T): void {
  this.map.set(id, value);
  - this.maxId = Math.max(this.maxId, id);
  + if (id > this.maxId_) {
  +
  + this.maxId_ = id;
  +
  + }
  +
  + }
  +
  + public get maxId(): number {
  +
  + return this.maxId_;
  }
  