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AP CSA 2015 Test Question 8 • 11 min read

Description

our notebook for the blog on Question 8

Overview of Question 8

Screenshot 2023-12-21 at 5 53 04 PM

Correct Answer: B

Our Answer: C

College Board Explanation:

Incorrect. This would be the result if the array results were assigned the products in the opposite order that they are calculated. In other words, for each value of j, the calculated product was assigned to result[result.length – 1 - j]. Correct. In the first iteration of the for loop, j is 0. The value of result[0] is assigned the product of row 1, column 0, which is 1 and row 0, column 2, which is 1. Therefore, result[0] is assigned the value 1. The second iteration of the for loop, when j is 1, result[1] is assigned the product of row 1, column 1, which is 2, and row 1, column 2, which is 3. Therefore, result[1] is assigned the value 6. The third iteration of the for loop, when j is 2, result[2] is assigned the product of row 1, column 2, which is 3, and row 2, column 2, which is 1. Therefore, result[2] is assigned the value 3. The final iteration of the for loop, when j is 3, result[3] is assigned the product of row 1, column 3, which is 4, and row 3, column 2, which is 1. Therefore, result[3] is assigned the value 4.

Consider the Following Method:

public static int[] operation(int[][] matrix, int r, int c)
{
    int[] result = new int[matrix.length];
    for (int j = 0; j < matrix.length; j++)
    {
        result[j] = matrix[r][j] * matrix[j][c];
    }
    return result;
}

The following code segment appears in another method in the same class:

// int[][] mat = {(3, 2, 1, 4),
    // ^ this line above is breaking the notebook
//    (1, 2, 3, 4),
//    (2, 2, 1, 2),
//    (1, 1, 1, 1)};

// int[] arr = operation(mat, 1, 2);
// Referring to integer mat
// Row 1 (r)
// Column 2 (c)

Which of the following represents the contents of arr as a result of executing the code segment?

a) [6, 4, 2, 4] b) [1, 6, 3, 4] c) [4, 3, 6, 1] d) [4, 4, 2, 2] e) [2, 2, 4, 4]

Code Segment

// public class Q8 {
//     public static void main(String[] args) {
//         // int[][] mat = {3, 2, 1, 4},
//         // ^ or it could be this
//             {1, 2, 3, 4},
//             {2, 2, 1, 2},
//             {1, 1, 1, 1}};

//         int[] arr = operation(mat, 1, 2);

//         for (int value : arr) {
//             System.out.print(value + " ");
//         }
//     }

//     public static int[] operation(int[][] matrix, int r, int c) {
//         int[] result = new int[matrix.length];
//         for (int j = 0; j < matrix.length; j++) {
//             result[j] = matrix[r][j] * matrix[j][c];
//         }
//         return result;
//     }
// }
// MatrixOperation.main(null)

Popcorn Hack

To make sure you understand the concept, please complete this question, even though it is the same code, the values of the rows and columns are different to show you understand the concept

Consider the Following Method:

public static int[] operation(int[][] matrix, int r, int c)
{
    int[] result = new int[matrix.length];
    for (int j = 0; j < matrix.length; j++)
    {
        result[j] = matrix[r][j] * matrix[j][c];
    }
    return result;
}

The following code segment appears in another method in the same class:

int[][] mat = {(2, 3, 4, 1),
    (4, 3, 2, 1),
    (1, 4, 3, 2),
    (2, 2, 2, 2)};

int[] arr = operation(mat, 2, 1);

Which of the following represents the contents of arr as a result of executing the code segment?

a) [6, 4, 2, 4] b) [1, 6, 3, 4] c) [4, 3, 6, 1] d) [4, 4, 2, 2] e) [2, 2, 4, 4]

public class Popcorn {
    public static void main(String[] args) {
        int[][] mat = {2, 3, 4, 1},
            {4, 3, 2, 1},
            {1, 4, 3, 2},
            {2, 2, 2, 2}};
        
        int[] arr = operation(mat, 2, 1);

        for (int value : arr) {
            System.out.print(value + " ");
        }
    }

    public static int[] operation(int[][] matrix, int r, int c) {
        int[] result = new int[matrix.length];
        for (int j = 0; j < matrix.length; j++) {
            result[j] = matrix[r][j] * matrix[j][c];
        }
        return result;
    }
}
Popcorn.main(null)
3 12 12 4