Implement a Deque (Double-Ended Queue)

To implement a Deque efficiently, I would first clarify if we need a fixed capacity or dynamic growth. Given IBM's focus on performance, I'd likely start with a circular array implementation for its superior cache locality. The core idea involves maintaining a front and rear index along with a count variable. For insertion at the front, we decrement the front index modulo the array size; for the back, we increment the rear index similarly. This ensures O(1) operations without shifting elements. We must handle the critical edge case where the array is full by checking if (count == capacity). Alternatively, a doubly linked list offers O(1) insertions and deletions at both ends without pre-allocating memory, though it incurs higher space overhead due to node pointers. In my previous project, I chose the circular array because our system required predictable memory usage and high throughput for log processing. By managing the modulo arithmetic correctly, we avoided buffer overflows and maintained consistent latency under heavy load, demonstrating that choosing the right underlying structure is as crucial as the algorithm itself.