AQA GCSE Computer Science June 2023 Paper 1, Question 14: completing a two-dimensional array algorithm

AQA 8525 June 2023 Paper 1, Question 14: fill three gaps in a pseudo-code subroutine that finds the highest vote in a two-dimensional array. Each gap explained, with the finished algorithm in Python to run and extend.

Past paper questionAQA 8525/1BJune 2023 Paper 13 marksComplete the algorithm

Question 14 of the AQA GCSE Computer Science Paper 1 sat on 19 May 2023 (8525/1B, the Python paper) shows an unfinished pseudo-code subroutine with three parts missing, labelled L1 to L3. This time there is no grid of options: you have to write the missing parts yourself. One mark each, 3 marks in all.

We do not copy the exam paper here. Open it beside this page: AQA June 2023 Paper 1B question paper (PDF). When you have finished, check the mark scheme too.

The question in short

Fifty students voted for their favourite kind of music. The results are in a two-dimensional array called results with two rows:

Row 0 holds the names. Row 1 holds the votes, stored as text.

A subroutine, showResults(method, numberOfGenres), should output the genre with the highest vote. It:

• sets pos to 0 and high to -1;
• if method is 'HIGHEST', loops i over the genres. It turns results[L1][i] into an integer called votes. If votes beats high, it stores votes in high and stores L2 in pos;
• otherwise outputs "not yet working";
• at the end, outputs the genre and the votes at position pos.

The main program asks the user for HIGHEST or LOWEST, stores the answer in method, and calls showResults(L3, 5).

Work it through

L1 is 1. The loop is reading votes, because it converts what it reads into an integer. The votes are in row 1. With a two-dimensional array written results[row][column], the row comes first.

L2 is i. When a new highest vote is found, the algorithm must remember where it was, so that it can output the matching name afterwards. The place is the loop counter, i. Look at the last output line for the proof: it uses results[0][pos] and results[1][pos], so pos is a column number.

L3 is method. The subroutine has two parameters. The second argument in the call is 5, the number of genres. The first must be the user's choice, which the line above stored in method.

The answers

Where the marks are lost

• 0 for L1. Row 0 holds the names. Turning "Pop" into an integer would crash.
• votes for L2. That would store 19 in pos, and there is no column 19. high remembers the value. pos remembers the place.
• 'HIGHEST' for L3. That would work for one choice only, and ignore what the user typed. Pass the variable.
• USERINPUT for L3. The input has already been read into method on the line before.

Run it

The same subroutine in Python. A two-dimensional array in Python is a list of lists. It prints each vote as it compares it.

from bugbot import *
connect()

# HIGHEST works. LOWEST is for you to write
METHOD = "HIGHEST"

def show_results(method, number_of_genres):
    results = [["Pop", "Post-Punk", "Techno", "Metal", "Dance"],
               ["7", "19", "14", "1", "9"]]
    pos = 0
    high = -1
    if method == "HIGHEST":
        for i in range(number_of_genres):
            votes = int(results[1][i])       # L1
            print("  ", results[0][i], votes)
            if votes > high:
                high = votes
                pos = i                      # L2
    else:
        print("not yet working")
    if high != -1:
        print(results[0][pos], "with", results[1][pos])

show_results(METHOD, 5)                      # L3 is the variable

Now change it

Finish the job the paper left undone. Make LOWEST work, so that it prints Metal with 1. You will need a second variable like high. What should it start at, given that there were 50 students?

Questions

What are the answers to AQA GCSE Computer Science 2023 Paper 1 Question 14?

L1 is 1, because the votes are in row 1 of the array. L2 is i, the position of the highest vote so far. L3 is method, the variable holding the user's choice.

How do you index a two-dimensional array?

Give two index numbers. In AQA pseudo-code and in Python, results[1][3] means row 1, column 3. Both start counting at 0.

Why does the algorithm start high at -1?

So that the first real vote is certain to beat it. No genre can have fewer than 0 votes, so -1 is lower than anything in the data. It also lets the algorithm tell whether a search has run at all.

More from this paper

• Question 6: Fill the gaps in a login routine 4 marks

Every AQA 8525 question we have worked

Learn it step by step

1. F3.5 Two-dimensional arrays Strings, lists and records
2. F4.2 Parameters and return values Functions and structured code

This is our own explanation of a published exam question. It is not written or endorsed by AQA, and the question paper and mark scheme remain AQA's copyright. Read them on AQA's site with the links on this page.