# 15.10. 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://apstudents.collegeboard.org/courses/ap-computer-science-a/free-response-questions-by-year.

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}

## 15.10.1. Try and Solve It¶

Complete the method getColumn below.

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