通过栈实现队列

[serendipityApe]

通过栈实现队列 lettcode上有一道相似的用两个栈实现队列 下面直接放答案吧

答案

// 添加一个辅助栈来实现队列;
class Queue {
  constructor(){
    var A=new Stack();
    var B=new Stack();
    this.A=A;
    this.B=B;
  }
  enqueue(element) { 
    this.A.push(element);
    // add new element to the rare
  }
  peek() { 
    if(this.A.size()==0 && this.B.size()!=0){
      return this.B.peek();
    }else if(this.B.size == 0){
      return -1;
    }
    while(this.A.size() !== 0){
      this.B.push(this.A.pop());
    }
    return this.B.peek();
    // get the head element
  }
  size() {
    return this.A.size()+this.B.size(); 
    // return count of element
  }
  dequeue() {
    if(this.A.size()==0 && this.B.size()!=0){
      return this.B.pop();
    }else if(this.B.size == 0){
      return -1;
    }
    while(this.A.size() !== 0){
      this.B.push(this.A.pop());
    }
    return this.B.pop();
    // remove the head element
  }
}