5.基于链表的队列

/* 
      基于链表的 - 队列
      尾部插入和头部删除
      先进先出
    */
    class LinkListQueue{
      constructor() {
        this.length = 0;
        this.head = null;
        this.tail = null;
      }
      // 入队
      enqueue(value){
        if(!this.tail) {
          this.head = this.tail = {value, next: null, prev: null};
        } else {
          this.tail.next = {value, next: null, prev: this.tail};
          this.tail = this.tail.next
        }
        this.length++;
      }
      // 出队
      dequeue() {
        let value;
        if(!this.head) return undefined;
        else{
          const value = this.head.value;
          if(!this.head.next){
            // 只剩最后一个了
            this.head = this.tail = null;
          } else {
            this.head.next.prev = null;
            this.head = this.head.next;
          }
          this.length--;
          return value;
        }
      }
    }
    const list = new LinkListQueue();
    list.enqueue(1);
    list.enqueue(2);
    list.enqueue(3);
    list.enqueue(4);
    console.log(list.dequeue());
    console.log(list);

算法总结：