Free Response - StringFormatter B

Section 4.42 Free Response - StringFormatter B

The following is a free response question from 2016. It was question 4 part B 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

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

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This question involves the process of taking a list of words, called wordList, and producing a formatted string of a specified length. The list wordList contains at least two words, consisting of letters only. When the formatted string is constructed, spaces are placed in the gaps between words so that as many spaces as possible are evenly distributed to each gap. The equal number of spaces inserted into each gap is referred to as the basic gap width. Any leftover spaces are inserted one at a time into the gaps from left to right until there are no more leftover spaces.

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The following three examples illustrate these concepts. In each example, the list of words is to be placed into a formatted string of length 20.

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Subsection 4.42.1 Part B

Write the StringFormatter method basicGapWidth, which returns the basic gap width as defined above.
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Assume that totalLetters works as specified regardless of what you wrote in part (a). You must use totalLetters appropriately to receive full credit.

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Complete method basicGapWidth below.

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/** Returns the basic gap width when wordList is used to produce
*  a formatted string of formattedLen characters.
*  Precondition: wordList contains at least two words, consisting of letters only.
*            formattedLen is large enough for all the words and gaps.
*/
public static int basicGapWidth(List<String> wordList,
                                 int formattedLen)

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Subsection 4.42.2 How to Solve Part B

To calculate basicGapWidth we need to find the number of spaces left after the characters fill the formattedLen and divide that by the number of gaps between words. We can use totalLetters (written in part A) to get the total number of characters for all the strings in wordList. The number of gaps between words is the number of words in wordList minus 1. The basicGapWidth is the number of spaces left divided by the number of gaps between words. Remember that if we do an integer division any fractional part will be thrown away, which is what we want to happen in this case.

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For example, if formattedLen is 20 and wordList is [“AP”, “COMP”, “SCI”, “ROCKS”] then the number of spaces left is 20 - 14 = 6 and the number of gaps is 4 - 1 = 3. The result is 6 / 3 = 2.

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If formattedLen is 20 and wordList is [“GREEN”, “EGGS”, “AND”, “HAM”] then the number of spaces left is 20 - 15 = 5 and the number of gaps is 4 - 1 = 3 so 5 / 3 = 1. There will be two extra spaces left over.

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If formattedLen is 20 and wordList is [“BEACH”, “BALL”] then the number of spaces left is 20 - 9 = 11 and the number of gaps is 2 - 1 = 1 so 11 / 1 = 11.

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Activity 4.42.1.

How do you access the number of items in an ArrayList<String> called list?

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list.length()
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.length() is used with Arrays to return the number of items. Try again!
list.size
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.size is a method call, so parentheses are required.
list.size()
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Correct! ArrayLists use .size() to return the number of items in a list.

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Activity 4.42.2.

True or False: A loop is required to correctly solve this problem.

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True
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Incorrect. You do not need to access any of the individual items in wordList.
False
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Correct! All you need is the size of wordList, which you can find without a loop.

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Subsection 4.42.3 Put the Code in Order

Activity 4.42.3.

The following has the correct code to solve this problem, but also contains extra code that isn’t needed in a correct solution. Drag the needed blocks from the left into the correct order on the right and indent them as well. Check your solution by clicking on the Check button. You will be told if any of the blocks are in the wrong or are in the wrong order. You will also be told if the indention is wrong.

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public static int basicGapWidth(List<String> wordList,
                                int formattedLen)
---
{
---
   int numSpaces = formattedLen - totalLetters(wordList);
   int numGaps = wordList.size() - 1;
---
   int numSpaces = formattedLen + totalLetters(wordList);
   int numGaps = wordList.length - 1; #paired
---
   return numSpaces / numGaps;
---
} //end method

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Subsection 4.42.4 Write the Code

Activity 4.42.4.

Finish writing the basicGapWidth method below so that it returns the size that the gap should be. The main method below will test your code to check that you solved it correctly.

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import java.util.*;

public class StringFormatter
{
    /**
     * Returns the basic gap width when wordList is used to produce a formatted
     * string of formattedLen characters. Precondition: wordList contains at least
     * two words, consisting of letters only. formattedLen is large enough for all
     * the words and gaps.
     */
    public static int basicGapWidth(List<String> wordList, int formattedLen) {}

public static int totalLetters(List<String> wordList)
    {
        int numLetters = 0;
        for (String s : wordList)
        {
            numLetters = numLetters + s.length();
        }
        return numLetters;
    }

public static void main(String[] args)
    {
        List<String> wordList = new ArrayList<String>();
        wordList.add("AP");
        wordList.add("COMP");
        wordList.add("SCI");
        wordList.add("ROCKS");
        System.out.println(
                "Should print 2 and prints: " + basicGapWidth(wordList, 20));

List<String> words2 = new ArrayList<String>();
        words2.add("GREEN");
        words2.add("EGGS");
        words2.add("AND");
        words2.add("HAM");
        System.out.println(
                "Should print 1 and prints: " + basicGapWidth(words2, 20));

List<String> words3 = new ArrayList<String>();
        words3.add("BEACH");
        words3.add("BALL");
        System.out.println(
                "Should print 11 and prints: " + basicGapWidth(words3, 20));
    }
}
====
import static org.junit.Assert.*;

import org.junit.*;

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

public class RunestoneTests extends CodeTestHelper
{

public RunestoneTests()
    {
        super("StringFormatter");
    }

@Test
    public void testMain() throws IOException
    {
        String output = getMethodOutput("main");
        String expect =
                "Should print 2 and prints: 2\n"
                        + "Should print 1 and prints: 1\n"
                        + "Should print 11 and prints: 11\n";

boolean passed = getResults(expect, output, "Expected output from main");
        assertTrue(passed);
    }

@Test
    public void test1()
    {
        List<String> wordList = new ArrayList<String>();
        wordList.add("AP");
        wordList.add("COMP");
        wordList.add("SCI");
        wordList.add("ROCKS");

String output = String.valueOf(StringFormatter.basicGapWidth(wordList, 20));
        String expect = "2";

boolean passed = getResults(expect, output, "basicGapWidth method test 01");
        assertTrue(passed);
    }

@Test
    public void test2()
    {
        List<String> words2 = new ArrayList<String>();
        words2.add("GREEN");
        words2.add("EGGS");
        words2.add("AND");
        words2.add("HAM");

String output = String.valueOf(StringFormatter.basicGapWidth(words2, 20));
        String expect = "1";

boolean passed = getResults(expect, output, "basicGapWidth method test 02");
        assertTrue(passed);
    }

@Test
    public void test3()
    {
        List<String> words3 = new ArrayList<String>();
        words3.add("SOCCER");
        words3.add("BALL");

String output = String.valueOf(StringFormatter.basicGapWidth(words3, 20));
        String expect = "10";

boolean passed = getResults(expect, output, "basicGapWidth method test on SOCCER, BALL");
        assertTrue(passed);
    }
}

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