Implementing queues and stacks with arrays

≈ 45 min

Implementing queues and stacks with arrays

A stack or queue can be built over an array, but the array does not remove the need for careful state. A stack tracks a top index. A queue tracks front, back and size, often using modular arithmetic so it can reuse positions at the beginning of a circular array. The implementation must make empty and full states unambiguous.

Underflow occurs when code pops or dequeues from an empty structure. Overflow occurs when a fixed-capacity structure cannot accept another item. Check these conditions before changing indices or returning a value. A clean interface can throw a documented exception or return a result that tells the caller no item is available.

Worked reasoning. In a circular queue of capacity 4, front points to the next removal and back points to the next insertion. After three enqueues and one dequeue, size is 2; the next enqueue may reuse the array position that the removed item occupied. Size avoids confusing a full queue with an empty queue when front equals back.

Exam lens. Draw the array indices and size after every operation. Explain the meaning of front and back in words before doing modular arithmetic.

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Which statement is the most defensible principle for Implementing queues and stacks with arrays?

An implementation must preserve its order contract and detect empty/full conditions before an operation breaks it.

Treat an implementation detail as more important than the stated rule.

Assume one successful run proves the system is correct in every case.

Avoid recording assumptions, limits or failure conditions.

Enter the key term for Implementing queues and stacks with arrays. What error occurs when code removes an item from an empty stack or queue?

Before calling pop() on a custom stack, what condition must the method check?

It must check that the stack is not empty so it does not underflow.

Use a larger class or broader permission without stating a rule.

Trust the first output and skip a boundary or failure check.

Hide the decision so affected people cannot inspect it.

Name the concise safeguard or principle that completes this lesson’s scenario: Before calling pop() on a custom stack, what condition must the method check?