Implement a Stack using Queues

To implement a stack using two queues, I would prioritize clarity and efficiency by choosing the 'expensive push' strategy, which keeps the pop operation constant time. This aligns well with Tesla's need for predictable latency in critical control loops. First, I maintain two queues, q1 as the primary storage and q2 as a helper. When pushing an element, I simply enqueue it into q1. For the pop operation, which requires removing the most recently added item, I transfer all elements except the last one from q1 to q2. Once q1 holds only the target element, I remove and return it. Then, I swap the names of q1 and q2 so q1 is ready for the next push. This ensures that the top of the stack is always at the front of the active queue for O(1) removal. Regarding complexity, push takes O(1) time, but pop becomes O(n) because we must move n-1 elements. Conversely, if I chose the alternative where push moves elements, push would be O(n) and pop O(1). Given that stacks often involve frequent pops during backtracking or undo operations, the first approach offers better worst-case guarantees for retrieval. I would also add a check for empty states before any operation to prevent runtime errors, ensuring robustness.