Stack and Queue in Python

Stack

A stack is a collection of elements that follows the Last In, First Out (LIFO) principle. This means that the last element added to the stack will be the first one to be removed.

Operations

• Push: Add an element to the top of the stack.
• Pop: Remove the top element from the stack.
• Peek/Top: View the top element without removing it.
• IsEmpty: Check if the stack is empty.

Example using a list

stack = []

# Push elements
stack.append(1)
stack.append(2)
stack.append(3)

print("Stack after pushing:", stack)

# Pop elements
print("Popped element:", stack.pop())
print("Stack after popping:", stack)

# Peek/Top element
print("Top element:", stack[-1])

# Check if stack is empty
print("Is stack empty?", len(stack) == 0)

Output

Stack after pushing: [1, 2, 3]
Popped element: 3
Stack after popping: [1, 2]
Top element: 2
Is stack empty? False

Queue

A queue is a collection of elements that follows the First In, First Out (FIFO) principle. This means that the first element added to the queue will be the first one to be removed.

Operations

• Enqueue: Add an element to the end of the queue.
• Dequeue: Remove the first element from the front of the queue.
• Front: View the first element without removing it.
• IsEmpty: Check if the queue is empty.

Example using collections.deque

from collections import deque

queue = deque()

# Enqueue elements
queue.append(1)
queue.append(2)
queue.append(3)

print("Queue after enqueuing:", queue)

# Dequeue elements
print("Dequeued element:", queue.popleft())
print("Queue after dequeuing:", queue)

# Front element
print("Front element:", queue[0])

# Check if queue is empty
print("Is queue empty?", len(queue) == 0)

Output

Queue after enqueuing: deque([1, 2, 3])
Dequeued element: 1
Queue after dequeuing: deque([2, 3])
Front element: 2
Is queue empty? False