Retired FRQ - Arrays - ArrayTester

Section 15.16 Retired FRQ - Arrays - ArrayTester - Part A

The following is a free response question from 2018. It was question 4 on the exam. You can see all the free response questions from past exams at Past AP CSA Exams.

🔗

Question 4. This question involves reasoning about arrays of integers. You will write two static methods, both of which are in a class named ArrayTester.

🔗

public class ArrayTester {
    /**
     * Returns an array containing the elements of column c of arr2D in the same order as they
     * appear in arr2D. Precondition: c is a valid column index in arr2D. Postcondition: arr2D is
     * unchanged.
     */
    public static int[] getColumn(int[][] arr2D, int c) {
        /* to be implemented in part (a) */
    }

    /**
     * Returns true if and only if every value in arr1 appears in arr2. Precondition: arr1 and arr2
     * have the same length. Postcondition: arr1 and arr2 are unchanged.
     */
    public static boolean hasAllValues(int[] arr1, int[] arr2) {
        /* implementation not shown */
    }

    /** Returns true if arr contains any duplicate values; false otherwise. */
    public static boolean containsDuplicates(int[] arr) {
        /* implementation not shown) */
    }

    /**
     * Returns true if square is a Latin square as described in part (b); false otherwise.
     * Precondition: square has an equal number of rows and columns. Precondition: square has at
     * least one row.
     */
    public static boolean isLatin(int[][] square) {
        /* to be implemented in part (b) */
    }
}

Part a. Write a static method getColumn, which returns a one-dimensional array containing the elements of a single column in a two-dimensional array. The elements in the returned array should be in the same order as they appear in the given column. The notation arr2D [r][c] represents the array at row r and column c.

🔗

The following code segment initializes an array and calls the getColumn method.

🔗

int [] [] arr2D = { { 0, 1, 2 }, { 3, 4, 5 }, { 6, 7, 8 }, { 9, 5, 3 }};
int[] result = ArrayTester.getColumn (arr2D, 1);

When the code segment has completed execution, the variable result result will have the following contents. result: {1, 4, 7, 5}

🔗

Subsection 15.16.1 Try and Solve It

Activity 15.16.1.

Complete the method getColumn below.

🔗

public class ArrayTester {

/**
     * Returns an array containing the elements of column c of arr2D in the same order as they
     * appear in arr2D. Precondition: c is a valid column index in arr2D. Postcondition: arr2D is
     * unchanged.
     */
    public static int[] getColumn(int[][] arr2D, int c) {
        /** Complete this method * */
    }

// Main method to test getColumn method
    public static void main(String[] args) {
        int[][] arr2D = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}, {9, 5, 3}};
        int[] result = ArrayTester.getColumn(arr2D, 1);
        System.out.println("It should print the values from the second column: 1 4 7 5.");
        for (int i = 0; i < result.length; i++) {
            System.out.print(result[i] + " ");
        }
    } // end of main
} // end of class
====
import static org.junit.Assert.*;

import org.junit.*;

import java.io.*;
import java.util.Arrays;

// import java.util.ArrayList;

public class RunestoneTests extends CodeTestHelper {
    public RunestoneTests() {
        super("ArrayTester");
        // CodeTestHelper.sort = true;
    }

@Test
    public void testMain1() {
        boolean passed = false;

String expect = "It should print the values from the second column: 1 4 7 5.\n1 4 7 5";

String output = getMethodOutput("main");

passed = getResults(expect, output, "Checking for expected output from main");
        assertTrue(passed);
    }

@Test
    public void testMain2() {
        boolean passed = false;

int[][] arr2D = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}, {9, 5, 3}};

String arrayStr = "[[0, 1, 2],\n [3, 4, 5],\n [6, 7, 8],\n [9, 5, 3]]";

int[] result = ArrayTester.getColumn(arr2D, 0);

String expect = "[0, 3, 6, 9]";
        String output = Arrays.toString(result);

passed =
                getResults(
                        expect,
                        output,
                        "Checking for expected output for getColumn(arr2D, 0)\n" + arrayStr);
        assertTrue(passed);
    }

@Test
    public void testMain3() {
        boolean passed = false;

int[][] arr2D = {{0, 1, 2, 3, 4, 5}, {6, 7, 8, 9, 5, 3}};

String arrayStr = "[[0, 1, 2, 3, 4, 5],\n [6, 7, 8, 9, 5, 3]]";

int[] result = ArrayTester.getColumn(arr2D, 2);

String expect = "[2, 8]";
        String output = Arrays.toString(result);

passed =
                getResults(
                        expect,
                        output,
                        "Checking for expected output for getColumn(arr2D, 0)\n" + arrayStr);
        assertTrue(passed);
    }
}

🔗

You have attempted of activities on this page.

🔗

Prev Top Next