Deque
Domain: Data Structures
🎯 Motivation
A deque (double-ended queue) lets you add and remove from both ends, combining stack and queue flexibility.
📋 Concrete Example
from collections import deque; d = deque([1,2,3]); d.appendleft(0); d.pop() gives 3. You can operate on both ends.
🔗 Analogy
A train with doors on both ends. Passengers can board or exit from either the front or the back of the train.