4.基于线性表的队列

/* 
      基于线性表的 - 队列
      尾部插入和头部删除
      先进先出
    */
    class ListQueue{
      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];
          }
        }
      }
      // 入队
      enqueue(value){
        this.arr[this.length] = value;
        this.length++;
        this.realloc();
      }
      // 出队
      dequeue() {
        if(!this.length) return undefined;
        const value = this.arr[0];
        for(let i = 0; i < (this.arr.length -1); i++){
          this.arr[i] = this.arr[i+1];
        }
        this.length--;
        this.realloc();
        return value;
      }
    }
    const list = new ListQueue();
    list.enqueue(1);
    list.enqueue(2);
    list.enqueue(3);
    list.enqueue(4);
    list.enqueue(5);
    console.log(list.dequeue());
    console.log(list);