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字典的实现

// 字典类function Dictionary () {    this.add = add;    this.dataStore = new Array();    this.find = find;    this.remove = remove;    this.showAll = showAll;    this.count = count;    this.clear = clear;}function add (key, value) {    this.dataStore[key] = value;}function find (key) {    return this.dataStore[key];}function remove (key) {    delete this.dataStore[key];}function showAll () {    let datakeys = Array.prototype.slice.call(Object.keys(this.dataStore));    for (let key in datakeys.sort()) {        console.log(`${datakeys[key]} -> ${this.dataStore[datakeys[key]]}`);    }}// 计数function count () {    let n = 0;    for (let key in Object.keys(this.dataStore)) {        ++n;    }    return n;}// 清空function clear () {    Object.keys(this.dataStore).forEach((key) => {        delete this.dataStore[key];    }, this);}

练习

使用Dictionary类写一个程序，该程序用来存储一段文本中各个单词出现的次数。该程序显示每个单词出现的次数，但每个单词只显示一次。比如下面一段话“the brown fox jumped over the blue fox”，程序的输出应为：

• the: 2
• brown: 1
• fox: 2
• jumped: 1
• over: 1
• blue: 1

function showWordCount (word) {    let d = new Dictionary();    let words = word.split(' ');    for (let i = 0, max = words.length; i < max; ++i) {        // 首次出现        if (typeof d.find(words[i]) === 'undefined') {            d.add(words[i], 1);        } else {            ++d.dataStore[words[i]];        }    }    Object.keys(d.dataStore).forEach((key) => {        console.log(`${key}: ${d.find(key)}`);    }, this);}// 示例showWordCount('the brown fox jumped over the blue fox');