一、题目

  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

  点击此处跳转题目。

二、C# 题解

  用哈希表存储查找，直接上代码：

public class WordsFrequency {private Dictionary<string, int> dic;public WordsFrequency(string[] book) {dic = new Dictionary<string, int>();foreach (string s in book) {if (dic.ContainsKey(s)) dic[s]++;else dic[s] = 1;}}public int Get(string word) {return dic.GetValueOrDefault(word, 0);}
}/*** Your WordsFrequency object will be instantiated and called as such:* WordsFrequency obj = new WordsFrequency(book);* int param_1 = obj.Get(word);*/

• 时间：492 ms，击败 100.00% 使用 C# 的用户
• 内存：93.49 MB，击败 80.00% 使用 C# 的用户