1. Dynamic Data Structures
Putting together variable size pieces
Copyright © Curt Hill

2. Introduction What are Dynamic Data Structures?
Data structures that may vary dynamically at run-time
This excludes ordinary arrays
Includes pointer based arrays, but this is just the tip of the ice berg
Not usually one pointer, but many
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3. Construction We can construct a variety of data structures
These come in many shapes and varieties
What they usually have in common is:
A class (or struct) referred to by a pointer
Also containing a pointer of similar or different type
Time to look at a picture
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4. Some D.D.S. Heap Stack D1 D3 D5 D2 NULL D4 NULL E9 E8 NULL NULL E7F2
F3,F4,F5
F12
F13,F14,F15 G6
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5. Commentary The shape of a dynamic data structure is limited only by:
Imagination
That a pointer must point at just one thing
There were three shapes in previous screen
Singly linked list
Unbalanced binary tree
An ad hoc shape with no classification
Each chunk (a class or struct) had data and some pointers
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6. More Commentary Various shapes are well known
Programmer may create any shape that makes sense
More discussion in next course
For the rest of this presentation lets consider the linked list
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7. Linked List
Consider the following class: class linked{ int i,j; double d; linked * next; … };
On the stack we have: linked * anchor;
What are the characteristics of this?
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8. Linked List Characteristics
A linked list is fully as powerful as an array
It may be faster or slower depending on how it is used
It may grow or shrink without reallocating the whole thing
Insertion and deletion are a snap
No disturbing adjacent members
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9. Linked List Picture anchor 3 5 1.4 1.1 4 7 2 7 1.7 9 5.3 -2 NULL 4.114 8
4.1
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10. Linked Lists and Arrays
The order of things in the list is dependent on how the pointers are organized
Not on the order of items in memory
Inserting an item in an array forces the movement of everything below it
If the array is full, it requires reallocation and copying everything
Insertion in a linked list only requires moving some pointers around
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11. Curt’s Pointer Rules for Classes
Every class that contains a pointer must have:
Default constructor
Copy constructor
Destructor
Operator overload of =
All of these will be generated by default
And generated wrong
Make them private if they should not be used
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12. Why?
The default constructor is needed to guarantee that the pointer is properly allocated
The copy constructor and assignment operator are used to prevent shallow copies
The destructor is needed to guarantee that no memory is lost
The whole data structure is deleted
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13. Deep and Shallow Copy
The problem with automatically generated copy constructor is that it will invariably do a shallow copy
We usually want a deep copy
What is the difference?
A shallow copy will usually just copy the pointer
A deep copy reproduces the entire structure
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14. Shallow list copy anchor1 … anchor1 … anchor2 anchor1 … anchor2
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15. One More Try
The last linked list contained two integers and a pointer in one class
Not usually the best practice
What is better is three classes:
The root of the list
One node on the list
An iterator
Several of these are friends of one another
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16. Three Classes LinkedList LinkedNode LinkedIterator
Will be the root of the list
It will contain all public methods
LinkedNode
One node
Private but makes others friends
LinkedIterator
Use to iterate through a list
Mutual friends with LinkedList
Needs to stop if list changes
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17. LinkedList
Lets consider: class LinkedList{ LinkedNode * root; LinkedList(LinkedList&) public: LinkedList(); bool add(int,char*); bool remove(int); char * find(int); };
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18. LinkedNode
Lets consider: class LinkedNode{ friend class LinkedList; friend class LinkedIterator; int key; char * data; LinkedNode * next; LinkedNode(); };
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19. LinkedIterator
Lets consider: class LinkedIterator{ LinkedNode * current; void changed(); public: LinkedIterator(); bool start(LinkedList*); bool next(int &, char *); bool more(); };
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