I knew what a circular queue was in the abstract but blanked on the fixed-capacity ring buffer framing until the interviewer nudged me toward it.
Start by clarifying the requirements and constraints, then explain the circular queue design using a fixed-size array with two pointers (front and rear) and a size counter. Walk through each operation, emphasizing how the modulo operator enables wrap-around and how the size counter distinguishes full from empty. Finally, discuss edge cases and complexity.
Pro tip: Mention that using a size counter avoids the classic ambiguity of full vs. empty when front equals rear, and that this design is lock-free friendly for concurrent scenarios. Also, briefly note that the same logic applies to a ring buffer in system design.
Ask about the expected capacity, data types, thread-safety, and whether dynamic resizing is needed. Confirm that all operations must be O(1) and that the queue is fixed-size.
Propose using a fixed-size array, two integer pointers (front and rear), and a size variable to track the number of elements. Explain that front points to the first element and rear points to the next insertion position.
For enQueue: check isFull, place element at rear, update rear = (rear + 1) % capacity, increment size. For deQueue: check isEmpty, retrieve element at front, update front = (front + 1) % capacity, decrement size. Front and Rear simply return the respective elements if not empty.
Test scenarios: empty queue, full queue, wrap-around, single element, and multiple enqueue/dequeue cycles. Ensure that front and rear are updated correctly and that size prevents overflow/underflow.
State that all operations are O(1) time and O(n) space. Optionally, mention how to make it thread-safe using locks or atomic operations, or how to implement a dynamic circular queue with resizing.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.