Download Dynamic Data Structures

Chapter 13
Dynamic Data
Structures
Dynamic Data Structure
• Dynamic data structure is a structure that can
expand and contract as a program executes.
• The creation and manipulation of dynamic data
structures requires use of pointers.
– A pointer is a variable which stores the memory
address of a data value.
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Comparison of Pointer and
Nonpointer Variables
• The actual data value of a pointer variable is
accessed indirectly.
• The actual data value of a nonpointer variable
can be accessed directly.
Pointer variable
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Nonpointer variable
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Pointer Review
• A call to a function with pointer parameters may
need to use the & operator.
• A pointer can be used to represent an array.
– e.g., char n[] is equal to char *n.
• A pointer can also represent a structure.
– e.g., File * is a pointer to a File structure.
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Pointer Review (Ex1)
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Pointer Review (Ex1 Cont.)
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Pointer Review (Ex2)
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Memory Allocation (1/3)
• C provides a memory allocation function called
malloc, which resides in the stdlib library.
– This function requires an argument which indicates
the amount of memory space needed.
– The returned data type is (void *) and should be
always cast to the specific type.
• E.g.,
Declaration:
int *nump; char *letp;
planet_t *planetp;
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Memory Allocation (2/3)
• Allocation:
nump = (int *) malloc(sizeof (int));
letp = (char *) malloc(sizeof (char));
planetp = (planet_t *) malloc(sizeof(planet_t));
• Assignment:
*nump = 307;
*letp = ‘Q’;
*planetp = blank_planet;
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Heap and Stack
• Heap is the region of memory where function
malloc dynamically allocates space for
variables.
• Stack is the region of memory where function
data areas are allocated and reclaimed.
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Memory Allocation (3/3)
Memory space after
allocation
Pointers
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Memory space after
assignment
Pointers
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malloc example
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Deallocating memory
• Function free deallocates memory—i.e., the
memory is returned to the system so that it can
be reallocated in the future.
• To free memory dynamically allocated by the
preceding malloc call, use the statement
• free( Ptr );
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Deallocating (free)
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Dynamic Array Allocation
• C provides a function calloc which creates an
array of elements of any type and initializes the
array elements to zero.
– Function calloc takes two arguments: the number
of array elements and the size of one element.
• E.g.,
int *array_of_nums;
array_of_nums = (int *)
calloc(10, sizeof(int));
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calloc example
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Linked List Basics
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Linked List
• A linked list is a sequence of nodes in which
each node is linked to the node following it.
• In C, each node can be represented by a struct:
typedef struct node_s{
char current[3];
int volts;
struct node_s *linkp;
}node_t;
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Creating Basic Nodes (1/2)
node_t *n1_p, *n2_p, *n3_p;
n1_p = (node_t *) malloc (sizeof(node_t));
strcpy(n1_p->current, “AC”);
n1_p->volts = 115;
n2_p = (node_t *) malloc (sizeof(node_t));
strcpy(n2_p->current, “DC”);
n2_p->volts = 12;
n3_p = n2_p;
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Creating Basic Nodes (2/2)
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Linking Two Nodes
• n1_p->linkp = n2_p;
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Chain access
• “n2_p->volts” is equal to
“n1_p-> linkp->volts”
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Three-Node Linked List
• n2_p->linkp = (node_t *)malloc(sizeof(node_t));
strcpy(n2_p->linkp->current, “AC”);
n2_p->linkp->volts = 220;
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Three-Element Linked List
• The end of a linked list is usually terminated with a null
pointer.
– n2_p->linkp->linkp = NULL;
– The following graph shows a complete linked list whose
length is three.
– The pointer variable n1_p points to the list head.
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Linked List After an Insertion
• We can easily insert or delete a node to or from a linked
list.
– The following graph shows an insertion of a new node
containing “DC 9” between the second and last nodes.
– Redirects the linkp of the new node to the last node.
– Redirects the linkp of the second node to the new node.
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Advantages of Linked Lists (1/2)
• A linked list is an important data structure because it can be
modified easily.
• For example, a new node containing DC 9 can be inserted
between the nodes DC 12 and AC 220 by changing only one
pointer value (the one from DC 12 ) and setting the pointer from
the new node to point to AC 220 .
• This means of modifying a linked list works regardless of how
many elements are in the list.
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Advantages of Linked Lists (1/2)
• Similarly, it is quite easy to delete a list element. Only one
pointer value within the list must be changed, specifically,
the pointer that currently points to the element being
deleted.
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Stack Basics
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Representing a stack with a linked list
•
•
•
•
Like a push down stack of books.
Push (insert) at top (pointed by Head)
Pop (remove) from the top (pointed by Head)
Last in first out (LIFO) architecture.
Head
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Push
7
restp
restp
5
restp
restp
3
restp
X
Pop
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Stacks
• A stack can be implemented as a constrained version
of a linked list.
• New nodes can be added to a stack and removed from
a stack only at the top.
• For this reason, a stack is referred to as a last-in, firstout (LIFO) data structure.
• A stack is referenced via a pointer to the top element
of the stack.
• The link member in the last node of the stack is set to
NULL to indicate the bottom of the stack.
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Stacks
• Stacks and linked lists are represented
identically.
• The difference between stacks and linked lists
is that insertions and deletions may occur
anywhere in a linked list, but only at the top of
a stack.
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Queue Basics
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Representing a Queue with a linked list
•
•
•
•
Like a queue of people waiting
Push at the Head (i.e at the end of the list).
Pop from the Bottom (i.e from the front of the list)
First In First Out (FIFO)
Head
Push
End
Front
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restp
restp
5
restp
restp
3
restp
X
Pop
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Queue Basics
• A queue is similar to a checkout line in a grocery
store—the first person in line is serviced first, and
other customers enter the line only at the end and wait
to be serviced.
• Queue nodes are removed only from the head of the
queue and are inserted only at the tail of the queue.
• For this reason, a queue is referred to as a first-in,
first-out (FIFO) data structure.
• The insert and remove operations are known as
enqueue and dequeue, respectively.
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Queue Applications (1/3)
• Queues have many applications in computer systems.
• For computers that have only a single processor, only
one user at a time may be serviced.
• Each entry gradually advances to the front of the
queue as users receive service.
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Queue Applications (2/3)
• Queues are also used to support print spooling.
• A multiuser environment may have only a
single printer.
• If the printer is busy, requests are spooled to
disk where they wait in a queue until the
printer becomes available.
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Queue Applications (3/3)
• Information packets also wait in queues in
computer networks.
• Each time a packet arrives at a network node,
it must be routed to the next node on the
network along the path to its final destination.
• The routing node routes one packet at a time,
so additional packets are enqueued until the
router can route them.
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Trees Basics
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Trees Basics
• Linked lists, stacks and queues are linear data
structures.
• A tree is a nonlinear, two-dimensional data
structure with special properties.
• Tree nodes contain two or more links.
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Trees Basics
• The root node is the first node in a tree.
• Each link in the root node refers to a child.
• The left child is the first node in the left subtree, and the
right child is the first node in the right subtree.
• A node with no children is called a leaf node.
• Computer scientists normally draw trees from the root node
down—exactly the opposite of trees in nature.
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Binary Tree
• We can extend the concept of linked list to binary trees
which contains two pointer fields.
– Leaf node: a node with no successors
– Root node: the first node in a binary tree.
– Left/right subtree: the subtree pointed by the left/right pointer.
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