Implement a Queue using Stack

JavaScript

hard

30 mins

A queue is a First-In-First-Out (FIFO) data structure. In this problem, you are to simulate a queue using only stacks (which are Last-In-First-Out, LIFO). Your task is to implement the enqueue, dequeue, and peek methods using stack operations.

enqueue(value) → Adds an element to the end of the queue.
dequeue() → Removes and returns the element from the front of the queue.
peek() → Returns the element at the front without removing it.
isEmpty() → Returns true if the queue is empty, else false.

Example Inputs & Outputs

const q = new QueueUsingStack();
q.enqueue(1);
q.enqueue(2);
q.enqueue(3);
q.dequeue();     // Output: 1
q.peek();        // Output: 2
q.isEmpty();     // Output: false

Constraints & Edge Cases

Only standard stack operations (push, pop, peek, length) are allowed.
All operations should have amortized O(1) time complexity.
Calling dequeue or peek on an empty queue should throw an error or return a clear indicator like null.
Support both integer and string data types as queue elements.