Queue
DSA · Beginner
Definition
A queue is a First-In-First-Out (FIFO) structure: add at the rear, remove from the front.
Queues power BFS, task scheduling, printers and message systems.
Diagram
Flowchart
Example: Queue with deque
from collections import deque
q = deque()
q.append('A'); q.append('B')
print(q.popleft())Output: A
Complexity
enqueue/dequeue O(1)
Key points
- FIFO order
- Circular queue reuses space
- Priority queue orders by priority
Interview questions
Why not use list.pop(0) in Python?
It is O(n); deque.popleft() is O(1).
Where is a queue used in graphs?
Breadth-First Search explores level by level using a queue.