14.10. 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 https://apstudent.collegeboard.org/apcourse/ap-computer-science-a/exam-practice.

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}

14.10.1. Try and Solve It

Complete the method getColumn below.

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