Statement

Given a Stack class with common operations such as push(), pop(), and isEmpty(), implement a Queue class with its enqueue(), dequeue(), and isEmpty() operations. The isEmpty() function should return true if the stack is empty and false otherwise.

Note: If the queue is empty, the dequeue() function should return −1-1.

A stack is a data structure in which objects are inserted and removed according to the LIFOLast In First Out principle, meaning the object that was most recently added to the stack is the first to be removed. There are two important functionalities of the stack:

  • push(): Inserts an item at the top of the stack.
  • pop(): Removes an item from the top of the stack and returns it.

A queue is a data structure in which objects are inserted and removed according to the FIFOFirst In First Out principle, meaning the object that has been in the queue longest is the first to be removed. There are two important functionalities of the queue:

  • enqueue(): Inserts an item at the back of the queue.
  • dequeue(): Removes an item from the front of the queue and returns it.

Example

Sample input

Enqueue(3), Dequeue(), Dequeue(), Enqueue(1), Enqueue(7), Dequeue()

Expected output

3, -1, 1

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