A queue is a FIFO (First-In-First-Out) data structure. Elements are added at the rear and removed from the front.
| Operation | Time |
|---|---|
| Enqueue / Dequeue | O(1) |
| Peek (front) | O(1) |
from collections import deque
q = deque()
q.append(10); q.append(20) # enqueue
q.popleft() # dequeue — 10
q[0] # peek frontA deque supports insertion and deletion from both ends.
from collections import deque
dq = deque([1, 2, 3])
dq.append(4); dq.appendleft(0) # add right/left
dq.pop(); dq.popleft() # remove right/left
dq.rotate(2) # rotate right by 2