BoxOfCandy free response answer 2023

BoxOfCandy is #4 from the from the 2023 AP Computer Science A Free Response problems.

https://apcentral.collegeboard.org/media/pdf/ap23-frq-comp-sci-a.pdf

Part (a) `moveCandyToFirstRow` method

public boolean moveCandyToFirstRow(int col)
{
    if(box[0][col] != null)
        return true;
    
    for(int r = 1; r < box.length; r++)
    {
        if(box[r][col] != null)
        {
            box[0][col] = box[r][col];
            box[r][col] = null;
            return true;
        }
    }
    
    return false;
}

Part (b) `removeNextByFlavor` method

public Candy removeNextByFlavor(String flavor)
{
    for(int r = box.length - 1; r >= 0; r--)
    {
        for(int c = 0; c < box[0].length; c++)
        {
            if(box[r][c] != null &&
                    box[r][c].getFlavor().equals(flavor))
            {
                Candy selected = box[r][c];
                box[r][c] = null;
                return selected;
            }
        }
    }
    
    return null;
}

I’ve receieved a few comments regarding my use of box[0] instead of box[r]. This is one of the situations in which I advise students to write code differently on the Exam than they would in a real program. box[0] works even if the loop with c is the outer loop. box[r] doesn’t. In a real program, that would be a compile time error. On the Exam, it could cost a point. On the AP CS A Exam, every row of a 2D array is guaranteed to have the same length.

Java files with test code

Candy.java includes a constructor and an implementation of getFlavor. FourTest.java includes JUnit 5 test code with the examples from the problem. See Running JUnit 5 tests.

Candy.java
BoxOfCandy.java
FourTest.java

2023 AP CS Exam Free Response Solutions

Additional 2D array resources

Help & comments

Get help from AP CS Tutor Brandon Horn

Comment on BoxOfCandy