Deque — Double-Ended Queue

A deque supports O(1) push/pop on both ends—strictly more flexible than a stack or queue alone.

Try this in Python

from collections import deque

d = deque([1, 2, 3])
d.appendleft(0)
d.append(4)
print(d.popleft(), d.pop(), list(d))

Key takeaways

• Great default structure for sliding windows and BFS deques.
• Name your ends (left/right) in comments for readability.
• Still not a priority queue—different abstract type.