DSA · Theory

Priority Queue using Doubly Linked List

Theory

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Priority Queue using Doubly Linked List is simple if you keep it on paper. Priya uses it for a ticket queue node in a counter.

For Priority Queue using Doubly Linked List, a dry-run table is in play. Don’t blame it until you have traced a ticket queue node.

Priority Queue using Doubly Linked List exists so Priya can keep a ticket queue node correct in a counter.

Priority Queue using Doubly Linked List shows up in a counter. Name a ticket queue node, not “a real-world scenario”.

If a ticket queue node breaks under Priority Queue using Doubly Linked List, check losing the next pointer on delete first.

Place Priority Queue using Doubly Linked List next to nearby DSA work — head → next → … is the link.

Viva for Priority Queue using Doubly Linked List: what it is → head → next → … → the mistake (losing the next pointer on delete).

Diagram

  front → [A][B][C] ← rear
  out ↑         ↑ in
       FIFO

Exam tip

Say Priority Queue using Doubly Linked List in one breath, then head → next → …, then losing the next pointer on delete.

from collections import deque

q = deque()
q.append(10)      # enqueue
q.append(20)
print(q.popleft())  # 10
print(list(q))

Priority Queue using Doubly Linked List — queue is FIFO. deque.popleft() is O(1).

DefPriority Queue using Doubly Linked List — Priya uses it for a ticket queue node in a counter.
RulePriority Queue using Doubly Linked List → head → next → ….
RememberPriority Queue using Doubly Linked List + a dry-run table (a counter).
UsePriority Queue using Doubly Linked List in a counter (a ticket queue node).
TrapPriority Queue using Doubly Linked List — losing the next pointer on delete.
ExPriority Queue using Doubly Linked List → a ticket queue node.