Basic Data Structures

1
Basic Data Structures

• Elementary Structures
• Arrays
• Lists

• Sequence Structures
• Stacks
• Queues

• Search Structures
• Binary search Tree
• Hash Tables

Graphs
2
What is a data structure?
A data structure (DS) is essentially a device
that collects and allows the manipulation of
data within the structure.

• DS Model (idea) operations

• Example A Stack
• Model A Stack
• Operations
• Add to stack
• Remove from stack
• check for empty
• look into stack
• empty the stack.
• Functionality specified using interface
• public interface Stack
• public void push(Object o)
• public Object pop()
• public Object peek()
• public boolean isEmpty()
• public void makeEmpty()

• A DS is independent of
• its implementation.

• In Java, use interface to
• specify operations of DS

• The interface describes the
• operation, but says nothing
• about its implementation.

3
Stack Structure
An array implementation of a Stack
max-1
public class StackArray impements Stack
private Objects s private int top
public StackArray(int size) s new
Objectsize top -1 public
void push(Object item) stop item
public Object pop()return stop-- public
Object peek()return stop public boolean
isEmpty()return (top-1) public void
makeEmpty()top -1 public boolean
isFull()return (tops.length-1)
top
3
3
2
1
0
4
Queue Structure
Implementation 1 Front always at array0
0
1
2
3

• DS A Queue
• Idea A Queue or a line
• Operations
• Add to the Queue
• Remove from the Queue
• peek at front element
• check for empty
• Make empty

front
back
Implementation 2 With wrap around.
public interface Queue public void
enQueue(Object x) public Object deQueue()
public boolean isEmpty() public void
makeEmpty() public Object peek()
0
1
2
back
front
Can overflow
5
Queue Structure
public class QueueCircularArray implements
Queue private Object q private int
front, back private int usedSpace
public QueueCircularArray(int size) q
new Objectsize front 0 back
size-1 usedSpace0 public void
enqueue(Object item) back
(back1)q.length qback item
usedSpace public Object dequeue()
Object item qfront qfront
null front (front1)q.length
usedSpace-- return item
public boolean isEmpty() (usedSpace0)
public boolean isFull() (usedSpaceq.length)
public Object peek()return qfront
6
What is a Dynamic Structure?
A data structure where there is no size
limitation.
Characteristics of dynamic structures

• Max size usually limited by machine memory
• Amount of memory used is a function of data
  stored in the structure.
• Data access is usually not random
• There is overhead involved in creating and
  maintaining such a structure

7
Fixed (or static) verses Dynamic structures
Static structures

• Disadvantages
• Fixed size results in either overflow or under
  use of internal resources.
• Resizing is a computationally expensive
  operation.
• Advantages
• Random/Direct access to data
• Usually easy to develop data structures using
  static structures

• Disadvantages
• Lose of random access.
• Usually harder to implement.
• Advantages
• No overflow or under use problems.
• Resizing is usually not expensive.

Dynamic Structures
8
Data Structure - a generic view
method1()
method2()
Implementation Either static of Dynamic
Interface
method3()
method4()
Example Queue
dequeue()
enqueue()
Array or dynamic implementation of queue
Methods of Queue
isEmpty()
makeEmpty()
9
Dynamic Structures - preliminaries
q
q new Integer(9)
Integer p Integer q
?
p new Integer(5)
p
p null
a1
p new Integer(6)
p
a2
qp
q p
p
a2
a2
q
10
Dynamic Structures - preliminaries
IntegerNode n1
public class IntegerNode private int item
private IntegerNode next public
IntegerNode(int item) setItem(item)
next null public void setItem(int
item) this.item item public
int getItem() return item
public void setNext(InegerNode next)
this.next next public IntegerNode
getNext() return next
n1 new IntegerNode(5)
5

IntegerNode n2 new IntegerNode(7)
7

n1.setNext(n2)
5
a2
7

11
Dynamic Structures - preliminaries
IntegerNode n3 n2 n2 n2.getNext()
n2 null
5
a2
7

n2.setNext(new IntegerNode(3)) n2 null
n2 n1.getNext()
n3.setNext(null)
n2.setNext(new IntegerNode(9))
12
A dynamic Stack
public class DStack implements Stack class
StackNode int data StackNode
next StackNode(int d)data d next
null //inner class private StackNode
top private int size public
DStack() Rules regarding
Constructors ALWAYS initialize instance
variables to null. public void
push(int d) Rules regarding adding to dynamic
structures Consider 2 cases Case 1
Adding to an empty structure Case 2 Adding
to the front of structure (maybe covered in 1)
Case 2 Inserting to an internal position.

13
A dynamic Stack
public int pop() Rules regarding removing
from a dynamic structure Case 1 Deleting a
root element Case 2 Deleting an internal
element
14
Traversing a Structure
Moving back and fourth along the structure.
Rules regarding traversing a structure 1. Never
move the reference pointing to the root of the
structure 2. Check for null before moving.
Traversing the structure below
Plain traversal
Printing the nodes in the structure
IntegerNode temp front while(temp ! null)
temp temp.getNext()
IntegerNode temp front while (temp!null)
Integer item temp.getItem()
System.out.println(item.toString()) temp
temp.getNext()
view animation!
15
Dynamic Queue
a4
enQueue()
3

deQueue()
isEmpty()
an
a1
back
front
makeEmpty()
peek()
Instance variables of class Queue
16
Dynamic Queue
public class DynamicQueue implements Queue
class ListNode //inner class int
data ListNode next ListNode(int
d, ListNode n) data d next
n private ListNode front
back public Queue() front null back
null
RULE Always initialize instance references
17
Dynamic Queue
public class DynamicQueue implements Queue
class ListNode //inner class int
data ListNode next ListNode(int
d) data d next null
private ListNode front back
public void enQueue(Object o) //Case 1-
adding the initial element ListNode n
new ListNode(o,null) if (front
null) //Case 2- adding
subsequent elements
18
Dynamic Linked List
a4
get()
3

remove()
a1
add()
front
search()
19
List Structure
List Structure
public Interface List public Object get(int
index) throws IndexOutOfBoundsException
public void remove(int index) throws
IndexOutOfBoundsException public void
add(Object item, int index) throws
IndexOutOfBoundsException public int
search(Object item) public boolean
isEmpty() public void makeEmpty()
public int size()
Cannot add/remove/get items beyond back
Can you implement this?
20
Dynamic Linked List
public class DList implements List class
ListNode int data ListNode
next ListNode(int o, ListNode n)
data o n next
private ListNode front public
List() public void add(Object o, int pos)
throws public Object get(int pos)
throws public void remove(int pos)
throws public int search(Object o)
public boolean isEmpty() public int
size() public void makeEmpty()

• Observe
• Inner class
• A single instance variable, front
• Clients view same for both dynamic and static
  implementations.

21
Dynamic Linked List
RULE Always initialize references to null or
other known value in all dynamic structures.
public class DList implements List class
ListNode int data ListNode
next ListNode(int o, ListNode n)
data o n next
private ListNode front public List()
front null
22
Dynamic Linked List
RULE When making a change to any dynamic
structure, treat changing a node referenced by a
named variable as special case.
public void add(Object o, int pos)
throws IndexOutOfBoundsException 0.
Check for exception case 1. Create a new
ListNode with o as the data 2. if
inserting at the front of the list, then
//named variable, front, changing!!!
3. Insert the new ListNode in front so as not to
lose the remaining elements
4. else //front, named
variable, does not change 5. traverse
to one-before the place to add 6.
Insert the new element in so as not to lose the
remaining list.
23
Dynamic Linked List
public class DList implements List
/ This method will add the data object o
into position pos in the list.
_at_param o the data item to be added _at_param
pos the position to which o should be added in
the list _at_exception IndexOutOfBoundsExcepti
on will be thrown if (poslt0) or (pos gt
size of the list) / public void add(int
o, int pos) throws
IndexOutOfBoundsException if (poslt0)(posgtsize()
) throw new IndexOutOfBoundsException() ListNode
n new ListNode(o,null) //create a new
node if (pos 0) //adding to front?
n.next(front) //add carefully! front
n else //adding internally ListNode
temp front //traverse for(int i0
iltpos-1 i) temp temp.next n.next
temp.next //insert in temp.next n
24
Dynamic Linked List
RULE When making a change to any dynamic
structure, treat making a change to a node
referenced by a named variable a special case.
public void remove(int pos)
throws IndexOutOfBoundsException 0.
Check for exception case 1. Remove the
first Node? //Named variable, front,
changing!!! 2. Remove so as not to lose the rest
of the list 3. else 4. Traverse to one before
the node to remove 5. Detach the node so as not
to lose the rest of the list
25
Dynamic Linked List
public class DList implements List /
The purpose of this method is to remove a
data object from the list at the given
position _at_param the item position to be
removed _at_exception IndexOutOfBoundsException
will be thrown if (poslt0) or
(posgtsize()) / public void remove(int
pos) throws IndexOutOfBoundsExc
eption if (poslt0)(posgtsize()) throw new
IndexOutOfBoundsException() ListNode temp if
(pos 0) //remove the first node? temp
front //carefully - so as not to lose front
front.next //the list! else //remove an
interior node ListNode n front //traverse for(
int i0 iltpos-1 i) n n.next temp
n.next n.next temp.next //remove temp.ne
xt null
26
Dynamic Linked List
public class DList public int
search(int target) IntegerNode temp
front int location 0 while
(temp!null) if (temp.getItem()
target) return location location
temp temp.getNext() return
-1 public boolean isEmpty() return (front
null) public int size() 1. traverse the list
counting the elements 2. return the
count public void makeEmpty() front null