队列是遵循先进先出 FIFO 原则的一组有序的项。
队列尾部添加新元素，并从顶部移除元素。最新添加的元素必须在队列末尾。

队列的方法

  • enqueue(element) 向队列发问添加新的元素
  • dequeue() 移除队列第一项并返回被除的元素
  • peek() / front() 返回队列第一个元素
  • isEmpty() 是否为空队列

  • size() 返回队列元素个数

    实现

    1. class Queue {
    2. constructor() {
    3.   this.count = 0;
    4.   this.lowestCount = 0;
    5.   this.items = {};
    6. }
    8. enqueue(element) {
    9.   this.items[this.count] = element;
    10.   this.count++;
    11. }
    13. dequeue() {
    14.   if (this.isEmpty()) {
    15.     return undefined;
    16.   }
    17.   const result = this.item[this.lowestCount];
    18.   delete this.items[this.lowestCount];
    19.   this.lowestCount++;
    20.   return result;
    21. }
    23. peek() {
    24.   if (this.isEmpty()) {
    25.     return undefined;
    26.   }
    27.   return this.items[this.lowestCount];
    28. }
    30. isEmpty() {
    31.   return this.size() === 0;
    32. }
    34. size() {
    35.   return this.count - this.lowestCount;
    36. }
    38. clear() {
    39.   this.items = {};
    40.   this.count = 0;
    41.   this.lowestCount = 0;
    42. }
    44. toString() {
    45.   if (this.isEmpty()) {
    46.     return '';
    47.   }
    48.   let objString = `${this.item[this.lowestCount]}`;
    49.   for (let i = this.lowestCount + 1; i < this.count; i++) {
    50.     objString = `${(objString, $this.items[i])}`;
    51.   }
    52.   return objString;
    53. }
    54. }
    1. const Queue = (function () {
    2. const _item = new WeakMap();
    4. return class Queue{
    5.   constructor() {
    6.     _item.set(this, []);
    7.   }
    9.   enqueue(element) {
    10.     _item.get(this).push(element);
    11.   }
    13.   dequeue() {
    14.     if (this.isEmpty()) {
    15.       return undefined;
    16.     }
    17.     return _item.get(this).shift();
    18.   }
    20.   front() {
    21.       return _item.get(this)[0];
    22.   }
    24.   peek() {
    25.     if (this.isEmpty()) {
    26.       return undefined;
    27.     }
    28.     return _item.get(this)[this.size() - 1];
    29.   }
    31.   isEmpty() {
    32.     return this.size() === 0;
    33.   }
    35.   size() {
    36.     return _item.get(this).length;
    37.   }
    39.   clear() {
    40.     _item.get(this).length = 0;
    41.   }
    43.   toString() {
    44.     if (this.isEmpty()) {
    45.       return '';
    46.     }
    48.     return _item.get(this).toString();
    49.   }
    50. };
    51. })();