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export default WordsFrequency;interface WordsFrequency {    get(word: string): number;}function WordsFrequency(book: string[]): WordsFrequency {    const storage = new Map<string, number>();    for (const word of book) {        storage.set(word, 1 + (storage.get(word) ?? 0));    }    function get(word: string): number {        return storage.get(word) ?? 0;    }    return { get };}