Notes on Queues in Data Structures

Introduction to Queues

• A queue is a FIFO (First In, First Out) data structure.
• Intuitive concept; prevalent in daily life (e.g., waiting in line).

Key Functions of Queues

• Enqueue: Adding an item to the end of the queue.
• Dequeue: Removing an item from the front of the queue.

Real-world Use Cases for Queues

• Situations where waiting occurs:
  • Bank tellers
  • Fast food orders (e.g., McDonald's)
  • DMV customer service
  • Supermarket checkout
• Important for modeling processes in computer programs.

Implementing Queues in Python

• Python has a built-in library called deque (double-ended queue).
• Allows adding/removing items from both ends.
• For simple queue operations, we focus on one end:
  • Append for adding items.
  • Pop left for removing items.

Importing deque

from collections import deque

Creating a Queue

• Create a new queue: my_queue = deque().
• Adding items to the queue:
  • Use append() function.
  • Example:
    • my_queue.append(5)
    • my_queue.append(10)

Removing items from the Queue

• Use popleft() to dequeue:
  • Example: my_queue.popleft() returns the first item (e.g., 5).

Conclusion

• Simple implementation of a queue in Python through deque.
• As an exercise, try writing a wrapper class for deque to create a single-ended queue using push and pop as a stack.