Deque Usage — Front and Back Patterns

Rotate windows, maintain monotonic candidates, or simulate a deck of cards—all are natural append/pop on either side.

Try this in Python

from collections import deque

d = deque(range(5))
d.rotate(2)
print(list(d))
while d:
    print(d.popleft() if len(d) % 2 else d.pop(), end=" ")
print()

Key takeaways

• rotate is O(k) for k steps—fine for small k, know the cost.
• Alternating pops teach double-ended control flow.
• Prefer explicit indices when rotation is huge.