3.基于链表的栈

/* 
      基于链表的 - 堆栈
      尾部插入和删除
    */
    class LinkListStack{
      constructor() {
        this.head = null;
        this.tail = null;
        this.length = 0;
      }
      push(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++;
      }
      pop() {
        let value;
        if(!this.tail) return undefined;
        else{
          const value = this.tail.value;
          if(!this.tail.prev){
            // 只剩最后一个了
            this.tail = this.head = null;
          } else {
            this.tail.prev.next = null;
            this.tail = this.tail.prev;
          }
          this.length--;
          return value;
        }
      }
    }
    const list = new LinkListStack();
    list.push(1);
    list.push(2);
    list.push(3);
    console.log(list.pop());
    console.log(list);

总结：