Data Structures in Python - Episode 6: Stacks and Queues

Data Structures in Python - Episode 6: Stacks and Queues

Introduction

Stacks and Queues are basic linear data structures used for organizing data. They are very useful in many programming scenarios like backtracking, resource scheduling, etc.

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1. Stacks (LIFO - Last In First Out)

Using a List as a Stack

# Stack operations
stack = []

# Push elements
stack.append('A')
stack.append('B')
stack.append('C')
print("Stack after pushes:", stack)

# Pop element
element = stack.pop()
print("Popped Element:", element)
print("Stack after pop:", stack)

Stack after pushes: ['A', 'B', 'C']
Popped Element: C
Stack after pop: ['A', 'B']

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2. Queues (FIFO - First In First Out)

Using deque from collections

from collections import deque

# Queue operations
queue = deque()

# Enqueue elements
queue.append('X')
queue.append('Y')
queue.append('Z')
print("Queue after enqueues:", queue)

# Dequeue element
element = queue.popleft()
print("Dequeued Element:", element)
print("Queue after dequeue:", queue)

Queue after enqueues: deque(['X', 'Y', 'Z'])
Dequeued Element: X
Queue after dequeue: deque(['Y', 'Z'])

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Quick Recap

Structure	Insertion	Removal	Python Tool
Stack	append()	pop()	List
Queue	append()	popleft()	deque

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Important Notes

Tip: Use deque from the collections module for fast queue operations.
Warning: Using list.pop(0) for queue behavior is inefficient (O(n) time).