What is the difference between the data structures 'stack' and 'queue'?

Stack — an abstract data type based on the LIFO (Last-In, First-Out) principle. The last added element will be the first to be retrieved.

Queue — an abstract data type based on the FIFO (First-In, First-Out) principle. The first added element will be the first to be retrieved.

Main operations:

Operation	Stack	Queue
Add	push() (usually at the end)	enqueue() (usually at the end)
Remove	pop() (from the end)	dequeue() (from the beginning)
View	peek() or top() (element at the end)	peek() or front() (element at the beginning)

Applications:

• Stack: function calls (call stack), syntax analysis, undo actions.
• Queue: task scheduling, buffer management (e.g., input-output), breadth-first traversal of graphs (BFS).

Implementation in Python:

For stack, you can use a list, adding and removing elements from the end:

# Stack using a list
stack = []
stack.append('a') # push
stack.append('b') # push
item = stack.pop() # pop

For queue, you can use collections.deque for efficient addition and removal from both ends:

# Queue using collections.deque
from collections import deque
queue = deque()
queue.append('a') # enqueue
queue.append('b') # enqueue
item = queue.popleft() # dequeue