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Doubly Linked List

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Doubly Linked List

Doubly Linked List sits in a counter. Vikram’s job is a ticket queue node. Write that first.

Do Doubly Linked List once by hand. head → next → …. Change one input. Say the new result out loud.

Without Doubly Linked List, a counter gets messy and a ticket queue node is hard to trust.

Vikram ships Doubly Linked List in a counter. That is the use case worth saying.

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

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

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

Diagram

  [10] → [20] → [30] → /
   head              tail

Exam tip

Board: a ticket queue node. Dry-run Doubly Linked List. Name the trap: losing the next pointer on delete.

Example

class Node:
    def __init__(self, val, next=None):
        self.val = val
        self.next = next

head = Node(1, Node(2, Node(3)))
cur = head
while cur:
    print(cur.val, end=" -> " if cur.next else "\n")
    cur = cur.next

Doubly Linked List — a linked list chains nodes with next pointers instead of contiguous indexes.

Short notes

DefDoubly Linked List — Vikram uses it for a ticket queue node in a counter.
RuleDoubly Linked List → head → next → ….
RememberDoubly Linked List + time vs memory (a counter).
UseDoubly Linked List in a counter (a ticket queue node).
TrapDoubly Linked List — losing the next pointer on delete.
ExDoubly Linked List → a ticket queue node.

class Node: def __init__(self, val, next=None): self.val = val self.next = next head = Node(1, Node(2, Node(3))) cur = head while cur: print(cur.val, end=" -> " if cur.next else "\n") cur = cur.next

Doubly Linked List

Example

Short notes

Questions

Doubly Linked List

Example

Short notes

Questions