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A-LevelComputer ScienceAbstract Data Types (ADTs)May/June 2025Paper 2 Q57 Marks

Stacks and queues are both abstract data types. A stack uses a top-of-stack pointer to indicate the location of the last item added to the stack. A queue uses two pointers: • a front pointer to indicate the location of the next item to be removed from the queue • a rear pointer to indicate the location of the next item to be added to the queue. A queue can be used to reverse the items stored on a stack. For example, if a stack contains six items: Initial state of the stack: top-of-stack pointer item 6 item 5 item 4 item 3 item 2 item 1 Final state of the stack when the items have been reversed: top-of-stack pointer item 1 item 2 item 3 item 4 item 5 item 6 Describe how the queue could be used to reverse the items that are currently stored on the stack. Your description must include how the pointers are used in both the stack and queue. Assume: • The stack initially contains an unknown number of items. • The queue can store all the items currently stored on the stack. • The queue is initially empty.

📋 Examiner Report & Trap Analysis

Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...

🎯 Mark Scheme Breakdown

Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.

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About This A-Level Computer Science Question

Topic

This structured question tests Abstract Data Types (ADTs) in A-Level Computer Science (syllabus code 9618). It is worth 7 marks.

Source

This question appeared in the Cambridge A-Level Computer Science May/June 2025 examination, Paper 2 Variant 1.

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