class Queue{ constructor(){ this.items = {}; this.front = 0; this.rear = 0; } push(item){ this.items[this.rear] = item; this.rear++; } pop(){ const item = this.items[this.front]; delete this.items[this.front]; this.front++; return item; } front(){ return this.items[this.front]; } size(){ retur..