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队列的实现

队列是一种先进先出的数据结构，常用于操作系统和网络编程中。以下是基于 JavaScript 的队列实现代码：

function Deque() {    this.dataStore = [];    this.enqueueFront = enqueueFront;    this.enqueueBack = enqueueBack;    this.dequeueFront = dequeueFront;    this.dequeueBack = dequeueBack;    this.front = function() {        return this.dataStore[0];    };    this.back = function() {        return this.dataStore[this.dataStore.length - 1];    };    this.toString = function() {        let retStr = '';        for (let i = 0; i < this.dataStore.length; i++) {            retStr += `${this.dataStore[i]}\n`;        }        return retStr;    };    this.empty = function() {        return this.dataStore.length === 0;    };}function enqueueFront(element) {    this.dataStore.unshift(element);}function dequeueFront() {    return this.dataStore.shift();}function enqueueBack(element) {    this.dataStore.push(element);}function dequeueBack(element) {    return this.dataStore.pop(element);}

练习一：修改队列类，形成一个双向队列

为了实现双向队列，我们可以对原队列类进行修改，使其支持从队列两端添加和删除元素。以下是修改后的代码：

function Deque() {    this.dataStore = [];    this.enqueueFront = enqueueFront;    this.enqueueBack = enqueueBack;    this.dequeueFront = dequeueFront;    this.dequeueBack = dequeueBack;    this.front = function() {        return this.dataStore[0];    };    this.back = function() {        return this.dataStore[this.dataStore.length - 1];    };    this.toString = function() {        let retStr = '';        for (let i = 0; i < this.dataStore.length; i++) {            retStr += `${this.dataStore[i]}\n`;        }        return retStr;    };    this.empty = function() {        return this.dataStore.length === 0;    };}function enqueueFront(element) {    this.dataStore.unshift(element);}function dequeueFront() {    return this.dataStore.shift();}function enqueueBack(element) {    this.dataStore.push(element);}function dequeueBack(element) {    return this.dataStore.pop(element);}

测试代码

let d = new Deque();d.enqueueFront('a');d.enqueueFront('b');d.enqueueFront('c');d.enqueueFront('d');d.enqueueFront('e');console.log(d.toString()); // 输出: e, d, c, b, ad.enqueueBack('a');d.enqueueBack('b');d.enqueueBack('c');d.enqueueBack('d');d.enqueueBack('e');console.log(d.toString()); // 输出: e, d, c, b, a, a, b, c, d, ed.dequeueFront();d.dequeueFront();console.log(d.toString()); // 输出: c, b, a, a, b, c, d, ed.dequeueBack();d.dequeueBack();d.dequeueBack();console.log(d.toString()); // 输出: c, b, a, a, b

练习二：判断单词是否是回文

使用双向队列，可以轻松判断一个单词是否为回文。以下是实现代码：

function isPalindrome(word) {    let d = new Deque();    for (let i = 0; i < word.length; i++) {        d.enqueueBack(word[i]);    }    while (d.dataStore.length > 1) {        if (d.dequeueFront() !== d.dequeueBack()) {            return false;        }    }    return true;}// 测试示例console.log(isPalindrome('racecar')); // trueconsole.log(isPalindrome('ada'));    // trueconsole.log(isPalindrome('mazey')); // false

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