AP Computer Science Exam Question - Multidimensional Arrays

Consider the following scenario:

You have been given a dataset that contains the scores of students in a classroom for three different subjects: Math, Science, and English. The dataset is represented using a two-dimensional array where each row represents a student and each column represents a subject.

int[][] scores = {
    {90, 85, 92},
    {78, 86, 80},
    {95, 88, 89},
    {82, 92, 86},
    {88, 90, 94}
};

Write a program in Java that calculates and outputs the average score for each subject.

Implement the following method:

/**
 * Calculates the average score for each subject.
 * 
 * @param scores a two-dimensional array representing the scores of students
 * @return an array of doubles with the average score for each subject
 */
public static double[] calculateAverage(int[][] scores) {
    // Write your code here
    
}

In your main method, call the calculateAverage method and print the resulting average scores for each subject.

Exemplary Output:

Average scores:
Math: 86.6
Science: 88.2
English: 88.2

Provide your implementation for the calculateAverage method, including a step-by-step explanation of your solution.

public static double[] calculateAverage(int[][] scores) {
    int numStudents = scores.length;
    int numSubjects = scores[0].length;
    
    double[] averages = new double[numSubjects];
    
    // Iterate over each column (subject)
    for (int subject = 0; subject < numSubjects; subject++) {
        int sum = 0;
        
        // Calculate the sum of scores for the current subject
        for (int student = 0; student < numStudents; student++) {
            sum += scores[student][subject];
        }
        
        // Calculate the average for the current subject
        double average = (double) sum / numStudents;
        
        // Store the average in the corresponding index of the averages array
        averages[subject] = average;
    }
    
    return averages;
}

Explanation:

1. We start by determining the number of students in the dataset by retrieving the length of the scores array, which represents the number of rows.
2. We also set numSubjects to the length of the first row, which represents the number of subjects.
3. We create a new array averages with a length equal to the number of subjects to store the average scores.
4. We iterate over each subject (column) using a for loop with the subject variable ranging from 0 to numSubjects-1.
5. Inside the outer loop, we initialize a variable sum to 0 to calculate the sum of scores for the current subject.
6. We then iterate over each student (row) using a for loop with the student variable ranging from 0 to numStudents-1.
7. Inside the inner loop, we add the score of the current student for the current subject to the sum variable.
8. After the inner loop finishes, we calculate the average for the current subject by dividing the sum by the number of students, casting the result to a double to ensure accuracy in the division.
9. Finally, we store the calculated average in the corresponding index of the averages array.
10. After the outer loop finishes, we return the averages array.
11. In the main method, we call the calculateAverage method and store the returned array of averages in a variable.
12. We then use a for loop to iterate over each index of the averages array and print the corresponding average score for each subject, along with the subject name.

Note: Make sure to include proper indentation and imports necessary to execute the code successfully.