Round is #3 from the from the 2025 AP Computer Science A Free Response problems.

https://apcentral.collegeboard.org/media/pdf/ap25-frq-computer-science-a.pdf

Part (a) Round constructor

public Round(String[] names)
{
    competitorList = new ArrayList<Competitor>();

    for(int i = 0; i < names.length; i++)
        competitorList.add(new Competitor(names[i], i + 1));
}

The first line, in which the instance variable competitorList is initialized, is often written incorrectly (ex: ArrayList<Competitor> competitorList = ...) or missed entirely. Initializing the instance variable to point to a new ArrayList is different than adding values to the list.

Part (b) buildMatches method

public ArrayList<Match> buildMatches()
{
    ArrayList<Match> matches = new ArrayList<Match>();

    int bestIndex = competitorList.size() % 2;
    int worstIndex = competitorList.size() - 1;

    while(bestIndex < worstIndex)
    {
        matches.add(new Match(
                competitorList.get(bestIndex),
                competitorList.get(worstIndex)));

        bestIndex++;
        worstIndex--;
    }

    return matches;
}

Java files with test code

Competitor.java
Match.java
Round.java
ThreeTest.java

See Running JUnit 5 tests.

2025 AP CS Exam Free Response Solutions

• DogWalker Free Response Solution
• SignedText Free Response Solution
• SumOrSameGame Free Response Solution

Help & comments

Get help from AP CS Tutor Brandon Horn

See an error? Question? Please comment below.

Comment on Round

2025-05-09 comment

(Email withheld)

for this question on Part B, instead of while loop (which now I feel like is a way better solution), on the test I used a nested for loop solution something like this (dont remember the whole thing):

for (int i = start; i < competitorList.size(); i++) {
    for (int j = competitorList.size() - 1; j > i; j--) {
        if (i == j) {
            return list;
        };
        // Match logic
    }
}

Do u think it will give me some credit or am I cooked? Btw, thank you so much for providing solutions!

Response

Assuming your comment // Match logic is where you’re making a Match object and adding it to the list: You are adding way too many Match objects to the list. Each competitor, potentially excluding the first, is supposed to be paired up with one other competitor, not all other competitors.

Your approach (though in a different order) is more appropriate for something like WordPairList (2018 #2) in which each word is paired with more than one additional word.

Thanks for reaching out.