考前速记

10 Second Recall

Node = {Data, NextPointer}
Head → first node
Tail → last node
Free → first available slot
-1 = null / end of list

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Traversal Cheat Sheet

Current ← Head
WHILE Current <> -1
    OUTPUT Node[Current].Data
    Current ← Node[Current].NextPointer
ENDWHILE

Three lines inside the loop (declare, output, advance) — never forget the advance line.

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Insert at End (7-mark answer)

Step	Code
Allocate	NewNode ← Free Free ← Node[Free].NextPointer
Store	Node[NewNode].Data ← Value Node[NewNode].NextPointer ← -1
Empty?	IF Head = -1 THEN Head ← NewNode Tail ← NewNode
Else	Node[Tail].NextPointer ← NewNode Tail ← NewNode

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Delete at Any Position

Step	Code
Search	Find target + predecessor via WHILE loop
Head case	Head ← Node[Head].NextPointer
Other case	Node[Previous].NextPointer ← Node[Current].NextPointer
Tail case	IF Current = Tail THEN Tail ← Previous
Free list	Node[Current].NextPointer ← Free Free ← Current

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Insert at Start

Node[NewNode].NextPointer ← Head
Head ← NewNode
IF Tail = -1 THEN Tail ← NewNode

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Common Edge Cases

Case	What to check
Empty list	Head = -1 → no traversal, separate insert path
Single node	Deletion → Head and Tail both become -1
Insert into empty	Both Head and Tail point to new node
Full free list	Free = -1 → no more nodes available (rarely tested)
Delete last node	Tail ← Previous (which may be -1)

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Pointer Rules

• Head only changes on insert-at-start or delete-at-start
• Tail only changes on insert-at-end or delete-at-end
• Free changes on every allocation and every return-to-free-list
• Node[i].NextPointer always holds an INTEGER index or -1

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Last-minute checklist

• TYPE Node has Data and NextPointer
• Traversal never modifies Head
• Free is updated when allocating
• Empty list case handled
• Node[NewNode].NextPointer set to -1 for end insertion
• Deleted node returned to free list
• Tail updated after deletion if needed

Exam Day

If you blank on a linked list question, write the traversal loop first — it earns 3–4 marks immediately and builds confidence.