using System;

using System.Collections.Generic;

using System.Linq;

public class Book

{

    public string Name;

    public Author[] Authors;

}

​

public class Author

{

    public string Name;

}

​

public class Program

{

    public static void Main()

    {

        var testData = TestDataset1;

        var keyword = "software";

        var booksWithKeyword = BooksWithWordInTitle(testData, keyword);

        Console.WriteLine($"Books with {keyword} in the title:");

        foreach(var book in booksWithKeyword)

        {

            Console.WriteLine($"\t{book.Name}");

        }

        Console.WriteLine("\n");

        var extractedAuthors = ExtractAuthors(testData);            

        foreach(var author in extractedAuthors)

        {

            Console.WriteLine(author.AuthorName);

            foreach(var book in author.BookNames)

            {

                Console.WriteLine($"\t{book}");

            }

            Console.WriteLine("\n");

        }

    }

    public static IEnumerable<Book> BooksWithWordInTitle(Book[] books, string wordToFind)

    {

        return books.Where(x => x.Name.ToLower().Split(" ").Contains(wordToFind));

    }

    public static (string AuthorName, string[] BookNames)[] ExtractAuthors(Book[] books)

    {

        return books

            .SelectMany(x => 

                        x.Authors.Select(a => new { 

                            BookName = x.Name, AuthorName = a.Name }))

            .GroupBy(x => x.AuthorName)

            .Select(x => (x.Key, x.Select(b=>b.BookName).ToArray()))

            .ToArray();

    }

    public static Book[] TestDataset1 = new[]{      

        new Book { Name = "Design Patterns: Elements of Reusable Object-Oriented Software", Authors = new[] { 

            new Author {Name = "Erich Gamma" }, 

            new Author {Name = "Richard Helm" },

            new Author {Name = "Ralph Johnson" },

            new Author {Name = "John Vlissides" },

            new Author {Name = "Grady Booch" }}},               

        new Book { Name = "Unified Modeling Language User Guide", Authors = new[] { new Author {Name = "Grady Booch" } } }, 

        new Book { Name = "The Annotated Turing", Authors = new[] { new Author {Name = "Charles Petzold" } } },

        new Book { Name = "Code: The Hidden Language of Computer Hardware and Software", Authors = new[] { new Author {Name = "Charles Petzold" } } },

        new Book { Name = "Balancing Agility and Discipline: A Guide for the Perplexed", Authors = new[] {          

            new Author {Name = "Barry Boehm" },

            new Author {Name = "Grady Booch" } } }      

    };

}