js实现队列的三种方法

使用数组实现队列

数组是最简单的队列实现方式，利用 push 和 shift 方法模拟队列的先进先出（FIFO）特性。

class ArrayQueue {
  constructor() {
    this.items = [];
  }

  enqueue(element) {
    this.items.push(element);
  }

  dequeue() {
    return this.items.shift();
  }

  peek() {
    return this.items[0];
  }

  isEmpty() {
    return this.items.length === 0;
  }

  size() {
    return this.items.length;
  }
}

使用链表实现队列

链表实现避免了数组 shift 操作的高时间复杂度（O(n)），enqueue 和 dequeue 均为 O(1)。

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
  }
}

class LinkedListQueue {
  constructor() {
    this.front = null;
    this.rear = null;
    this.size = 0;
  }

  enqueue(value) {
    const newNode = new Node(value);
    if (this.rear === null) {
      this.front = newNode;
      this.rear = newNode;
    } else {
      this.rear.next = newNode;
      this.rear = newNode;
    }
    this.size++;
  }

  dequeue() {
    if (this.front === null) return null;
    const removedValue = this.front.value;
    this.front = this.front.next;
    if (this.front === null) this.rear = null;
    this.size--;
    return removedValue;
  }

  peek() {
    return this.front?.value;
  }

  isEmpty() {
    return this.size === 0;
  }
}

使用两个栈实现队列

通过两个栈（输入栈和输出栈）模拟队列行为，enqueue 直接压入输入栈，dequeue 时从输出栈弹出。

class StackQueue {
  constructor() {
    this.inStack = [];
    this.outStack = [];
  }

  enqueue(element) {
    this.inStack.push(element);
  }

  dequeue() {
    if (this.outStack.length === 0) {
      while (this.inStack.length > 0) {
        this.outStack.push(this.inStack.pop());
      }
    }
    return this.outStack.pop();
  }

  peek() {
    if (this.outStack.length === 0) {
      while (this.inStack.length > 0) {
        this.outStack.push(this.inStack.pop());
      }
    }
    return this.outStack[this.outStack.length - 1];
  }

  isEmpty() {
    return this.inStack.length === 0 && this.outStack.length === 0;
  }
}