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Algorithmsqueue fifo principle

Queue FIFO Principle

TT
Testlaa Team
May 14, 2026•1 min read

A queue is first-in-first-out (FIFO): service order matches arrival order at a single service point.

Try this in Python

from collections import deque

q: deque[int] = deque()
q.append(1)
q.append(2)
q.append(3)
print(q.popleft(), q.popleft(), q.popleft())

Key takeaways

  • deque gives O(1) on both ends—perfect for learning queues in Python.
  • list.pop(0) works but is O(n); avoid it in hot paths.
  • FIFO is the default mental model for BFS frontiers.

Tags:

Stacks & queuesPythonStudents