考纲要点

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9618 Syllabus Extract — Queue ADT

考点	要求	常见题型
Define a queue as an abstract data type	Understand FIFO principle	Theory (Q1)
Implement a circular queue using a static array	Fixed-size array + pointers	Practical (6–12 marks)
Enqueue operation with wrap-around	MOD operator	Code writing (6 marks)
Dequeue operation with wrap-around	MOD operator	Code writing (6 marks)
Distinguish full vs empty states	NumberOfItems counter	Code + explanation (2–3 marks)
Initialise queue structure	Pointers at -1, items at None	Code (1–2 marks)

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必须掌握的能力

1. Write Enqueue procedure from scratch
2. Write Dequeue function from scratch
3. Write IsFull / IsEmpty boolean functions
4. Trace a circular queue through multiple enqueue/dequeue operations
5. Explain why NumberOfItems is needed (not just pointer comparison)
6. Identify when a queue is circular (look for MOD, NumberOfItems)

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考试常见设问方式

设问	分值	提示词
"Write a procedure to add an item to the queue"	6	Enqueue, AddItem, Insert
"Write a function to remove and return an item"	6	Dequeue, RemoveItem, Pop
"State what is meant by a circular queue"	2	Explanation, diagram
"Explain why NumberOfItems is needed"	2	Full vs empty ambiguity
"Amend the linear queue to be circular"	4	Add MOD, add counter

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与 Linear Queue 的考点对比

Aspect	Linear Queue考点	Circular Queue考点
Pointer update	+ 1 only	(+ 1) MOD Size
Full condition	Tail == Size - 1	NumberOfItems == Size
Empty condition	Head == Tail	NumberOfItems == 0
Space reuse	❌ Not tested	✅ Key feature
Harder question	Resizing	Wrap + counter logic

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考纲分析

The circular queue typically appears in Section A of Paper 4 (Q1 or Q2). It is one of the most predictable 6-mark questions. The exam routine is almost always: "Write a procedure to enqueue an item into a circular queue" or "Write a function to dequeue an item from a circular queue".

Master this topic — it is a guaranteed 6 marks.