1. Single Pointer Implemention
Lists
ADT
Array Implementation
Single Pointer Implemention
Cursors
Doubly Linked Ring
9/21/2018
CS 303 –Lists
Lecture 4

2. ADT List - Operations L = MakeNull() Insert(L,p,x) Delete(L,p)
p = First(L) p = End(L)
p = Previous(L,p) p = Next(L,p)
p = Locate(L,x)
x = Retrieve(L,p)
x: ElementType
p: PositionType
L: ListType
Why isn’t First(L)always 1?
Because Position is hidden! No arithmetic is allowed (by the user) on
Positions. Use Previous and Next!
9/21/2018
CS 303 –Lists
Lecture 4

3. Array Implementation a1 a2 1 2 n an MaxLength Last
Internal routines can do arithmetic on “positions”, but external (user) routines cannot. Why?
9/21/2018
CS 303 –Lists
Lecture 4

4. Single Pointer Implementation
??? a1 a2
... an
Header
What is the purpose of the header? (Hing: consider “position”)
Compare details (efficiency, behavior of “position”) with Array Implementation
Array Pointer
Previous/End EASY HARD
Insert/Delete HARD EASY
9/21/2018
CS 303 –Lists
Lecture 4

5. Cursors (an aside)
Suppose you want to use pointers – but your programming
environment does not support them?
Use “cursors”
Allocate an Array called CursorSpace
Use indices into CursorSpace just like pointers
Do your own memory management of cells
New
Dispose
9/21/2018
CS 303 –Lists
Lecture 4

6. Doubly Linked Lists/Rings? a? an
Many variations
Is ‘?’ a0 (Header) or a1? [a1]
Is ‘L’ part of the structure, or an external pointer? [external]
Is there a “First” element? [where L points!]
Implement the full Ring!
Everything is EASY; Position is natural
9/21/2018
CS 303 –Lists
Lecture 4