Introduction: From Stack to Queue - Educational Content

Contrasting the LIFO Stack with the FIFO Queue.

While we have previously examined the Stack, characterized by its LIFO (Last-In, First-Out) principle, our focus now shifts to the Queue.
A Queue strictly follows the FIFO (First-In, First-Out) principle: the first element to enter is the first to be removed.
Unlike a Stack's single 'top' pointer, a Queue uses two pointers: front for removal and rear for insertion.
The core operations are enQueue (add to rear) and deQueue (remove from front).

Stack vs. Queue Properties

Property	Stack	Queue
Principle	LIFO (Last-In, First-Out)	FIFO (First-In, First-Out)
Access Points	One (Top)	Two (Front & Rear)
Add Operation	Push	Enqueue
Remove Operation	Pop	Dequeue

Queue Abstract Interface (Python)

1# Abstract definition of the Queue interface
2class QueueInterface:
3    """Defines the core FIFO operations."""
4    
5    def enQueue(self, item):
6        """Adds item at the rear index."""
7        pass
8
9    def deQueue(self):
10        """Removes and returns item from the front index."""
11        pass
12
13    def peek(self):
14        """Inspects the element at the front without removing it."""
15        pass

Knowledge Check

Which fundamental principle does a standard Queue strictly follow?

A) LIFO (Last In, First Out)
B) LILO (Last In, Last Out)
C) FIFO (First In, First Out)
D) HIFO (Highest In, First Out)