js -面试题 16.02. 单词频率

设计一个方法，找出任意指定单词在一本书中的出现频率。

你的实现应该支持如下操作：

WordsFrequency(book)构造函数，参数为字符串数组构成的一本书
get(word)查询指定单词在书中出现的频率
示例：

WordsFrequency wordsFrequency = new WordsFrequency({“i”, “have”, “an”, “apple”, “he”, “have”, “a”, “pen”});
wordsFrequency.get(“you”); //返回0，"you"没有出现过
wordsFrequency.get(“have”); //返回2，"have"出现2次
wordsFrequency.get(“an”); //返回1
wordsFrequency.get(“apple”); //返回1
wordsFrequency.get(“pen”); //返回1
提示：

book[i]中只包含小写字母
1 <= book.length <= 100000
1 <= book[i].length <= 10
get函数的调用次数不会超过100000

来源：力扣（LeetCode）

/**
 * @param {string[]} book
 */
var WordsFrequency = function(book) {
            this.map = new Map();
            for (const item of book) {
                this.map.set(item, (this.map.get(item) || 0) + 1);
            }
};

/** 
 * @param {string} word
 * @return {number}
 */
WordsFrequency.prototype.get = function(word) {
return this.map.get(word) || 0;
};

/**
 * Your WordsFrequency object will be instantiated and called as such:
 * var obj = new WordsFrequency(book)
 * var param_1 = obj.get(word)
 */