Dynamic Data
Structures
Putting together variable size
pieces
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
Some D.D.S.
Heap
Stack
D1
D3
D2
E9
E8
D5
NULL
D4
NULL
NULL
E4
F2
E7
E2
NULL
NULL
E3
NULL
F3,F4,F5
F12
F13,F14,F15
G6
Copyright © 2006-2009 Curt Hill
NULL
NULL
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
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
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?
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
Linked List Picture
1.4
5
3
1.1
7
4
anchor
2
7
1.7
-2
9
5.3
NULL
14 8
4.1
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
Shallow list copy
anchor1
…
anchor1
…
anchor2
anchor1
…
anchor2
Copyright © 2006-2009 Curt Hill
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
Copyright © 2006-2009 Curt Hill
Three Classes
• LinkedList
– 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
Copyright © 2006-2009 Curt Hill
LinkedList
• Lets consider:
class LinkedList{
LinkedNode * root;
LinkedList(LinkedList&)
public:
LinkedList();
bool add(int,char*);
bool remove(int);
char * find(int);
};
Copyright © 2006-2009 Curt Hill
LinkedNode
• Lets consider:
class LinkedNode{
friend class LinkedList;
friend class LinkedIterator;
int key;
char * data;
LinkedNode * next;
LinkedNode();
};
Copyright © 2006-2009 Curt Hill
LinkedIterator
• Lets consider:
class LinkedIterator{
LinkedNode * current;
void changed();
public:
LinkedIterator();
bool start(LinkedList*);
bool next(int &, char *);
bool more();
};
Copyright © 2006-2009 Curt Hill