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面试题 16.02. 单词频率

English Version

题目描述

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)查询指定单词在数中出现的频率

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

解法

计数器实现。

Python3

class WordsFrequency:

    def __init__(self, book: List[str]):
        self.counter = Counter(book)

    def get(self, word: str) -> int:
        return self.counter[word]

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

Java

class WordsFrequency {

    private Map<String, Integer> counter = new HashMap<>();

    public WordsFrequency(String[] book) {
        for (String word : book) {
            counter.put(word, counter.getOrDefault(word, 0) + 1);
        }
    }

    public int get(String word) {
        return counter.containsKey(word) ? counter.get(word) : 0;
    }
}

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

JavaScript

/**
 * @param {string[]} book
 */
var WordsFrequency = function (book) {
    this.counter = {};
    for (const word of book) {
        this.counter[word] = (this.counter[word] || 0) + 1;
    }
};

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

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

TypeScript

class WordsFrequency {
    private map: Map<string, number>;

    constructor(book: string[]) {
        const map = new Map<string, number>();
        for (const word of book) {
            map.set(word, (map.get(word) ?? 0) + 1);
        }
        this.map = map;
    }

    get(word: string): number {
        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)
 */

Rust

use std::collections::HashMap;
struct WordsFrequency {
    counter: HashMap<String, i32>
}


/**
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl WordsFrequency {

    fn new(book: Vec<String>) -> Self {
        let mut counter = HashMap::new();
        for word in book.into_iter() {
            *counter.entry(word).or_insert(0) += 1;
        }
        Self { counter }
    }

    fn get(&self, word: String) -> i32 {
        *self.counter.get(&word).unwrap_or(&0)
    }
}

/**
 * Your WordsFrequency object will be instantiated and called as such:
 * let obj = WordsFrequency::new(book);
 * let ret_1: i32 = obj.get(word);
 */

...