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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, a
d.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, e
d.dequeueFront();
d.dequeueFront();
console.log(d.toString()); // 输出: c, b, a, a, b, c, d, e
d.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')); // true
console.log(isPalindrome('ada'));    // true
console.log(isPalindrome('mazey')); // false

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