2.基于线性表的栈

/* 
      基于线性表的 - 堆栈
      尾部插入和删除
    */
    class ListStack{
      constructor() {
        this.arr = new Array();
        this.length = 0;
        this.size = 10;
        this.realloc = () => {
          let new_arr;
          if(this.length === this.size) {
            // 满了 增加内存
            this.size = this.size*2;
            new_arr = new Array(this.size);
          } else if(this.size > 10 && this.length <= Math.floor(this.size /4)) {
            this.size = Math.floor(this.size /2);
            new_arr = new Array(this.size);
          }
          if(new_arr) {
            this.arr.forEach((v, i) => {
              new_arr[i] = v;
            });
            this.arr = [...new_arr];
          }
        }
      }
      push(value){
        this.arr[this.length] = value;
        this.length++;
        this.realloc();
      }
      pop() {
        if(this.length === 0) {
          return undefined;
        }
        const value = this.arr[this.length -1];
        delete this.arr[this.length -1];
        this.length--;
        this.realloc();
        return value;
      }
    }
    const list = new ListStack();
    list.push(1);
    list.push(2);
    list.push(3);
    list.push(4);
    list.push(1);
    list.push(2);
    list.push(3);
    list.push(4);
    list.push(1);
    list.push(2);
    list.push(3);
    list.push(4);
    console.log(list.pop());
    console.log(list.pop());
    console.log(list.pop());
    console.log(list.pop());
    console.log(list.pop());
    console.log(list.pop());
    console.log(list.pop());
    console.log(list);