Ace the AP Computer Science Exam for High Schoolers/

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Solution Review

Solution Review

Let’s look at the solution to the tasks from the previous lesson.

We'll cover the following...

Task I: Total number of books by an author

The task was to find the total number of books written by an author. Look at the code below.

Java
public class driver 
{
    public static int authorBooks(String author, String[][] dataset)
    {
        // Creating an ArrayList to keep books
        ArrayList<String> book = new ArrayList<String>();
        for(int i=0; i<dataset.length; i++)  // traversing the whole dataset
        {
            /* If the name of the book’s author matches with the given author, and
            the ArrayList doesn't already contain this book, then we add this book to the ArrayList
            */ 
            if(dataset[i][1].equals(author) && !book.contains(dataset[i][0]))
                book.add(dataset[i][0]);
        }
        return book.size();               // returning the size of array list
    }
    public static void main(String args[]) 
    {
        reader r = new reader();    // A helper class designed to read data    
        // Calling func that reads data from data.csv and returns in a 2D matrix                
        String[][] dataset= r.readDataset("data.csv"); 
        
        // Call to the function
        System.out.print(authorBooks("Bill O'Reilly", dataset));                          
    }  
}

Look at the header of the authorBooks method at line 3. We make an ArrayList variable, book, at line 6. Then, we traverse all rows of the dataset with a for loop.

Look at line 13. If a record’s author matches with the given author (argument passed), and we haven’t already added the book’s name of that record in book, then we add the book’s name of that record in book.

Lastly, we return the size of book, which is the number of books written by the author.

Task II: All the authors in the dataset

The task was to find the names of all the authors present in the dataset. Look at the code below.

Java
public class driver 

{

    public static ArrayList<String> allAuthors(String[][] dataset)

    {

        // Creating an ArrayList to store the names of the authors

        ArrayList<String> author = new ArrayList<String>();



        for(int i=1; i<dataset.length; i++)    // traversing thw whole dataset

        { 

            // If the author is not already present in the ArrayList authors, then we add their name to the ArrayList

            if(author.contains(dataset[i][1]) == false)

                author.add(dataset[i][1]);

        }

        return author;  // returning the authors' list

    }



    public static void main(String args[]) 

    {

        reader r = new reader();    // A helper class designed to read data    



        // Calling func that reads data from data.csv and returns in a 2D matrix                

        String[][] dataset= r.readDataset("data.csv"); 

        

        // Call to the function

        for(String author: allAuthors(dataset))

            System.out.println(author);                          

    }  

}

Look at the header of the allAuthors method at ...