Stack and Queue
1
• Stack (Array Implementation)
• Queue (Array Implementation )
2
Stack
What is a Stack?
1) It is a data structure for storing some values
2) It is an ADT.
3) Implemented using Arrays or Linked List
4) used in Operating System and in System
Programming
3
Stack
How to Store and Retrieve from a Stack?
1) All Insertions ( Storing) and Deletions (Removing)
of entries are made at one end called the TOP of Stack
2) Last item added to a stack (PUSH) is always the first
that will be removed (POP) from the stack.
3) This property is called Last In First Out also known
as LIFO
4) The operations are done with a single pointer to the
top of list of elements.
Operations... 4
Stack
F
D
G
TOP
E
EG - Plates
C
Books
B
(LIFO)
A
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Operations
• There are Four operations :
1) Push ( )
used to add the data at the top of the stack.
Check whether the stack is full or not
2) Pop ( )
used to remove data at the top of the stack.
Check whether the stack is empty or not
3) Empty ( )
Checks whether stack is empty, TOP = -1
4) Full ( )
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checks whether stack is full, TOP = maxstacksize
Stack - implementation
• Uses ARRAY to represent a stack
Class stack
{ private :
int stackelement[10],TOP;
public:
stack( ) { top = -1}
int Empty( );
void push(int);
int Full ( );
};
int Pop( );
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Stack
How to Push?
Void stack :: Push(int data2add)
{ if (!Full( ))
{ TOP++;
Stackelement[TOP] = data2add;
}
else
cout << “Stack is Full!!!”<<endl;
}
8
Stack
How to Pop?
Int stack :: Pop( )
{int data2remove;
if (!Empty( ))
{ data2remove = Stackelement[TOP];
TOP--;
return data2remove; }
else{ cout << “Stack is Empty!!!”<<endl;
return 0;
} }
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Stack
How to check for full?
Int Stack :: Full( )
{
if (TOP==9) return 1;
else return 0;
}
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Stack
How to check for Empty?
Int Stack :: Empty( )
{
if (TOP== -1) return 1;
else return 0;
}
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Stack
Void main( )
{
stack stackobj;
stackobj.Push(23);
stackobj.Push(46);
stackobj.Push(37);
stackobj.Push(10);
stackobj.Push(55);
cout << stackobj.Pop( );
cout << stackobj.Pop( );
}
55
10
55
37
46
23
10
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Applications of Stack
We shall see two applications of the stack
1) Use of Stacks in Function Calls
2) Palindrome Checking
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Use of Stacks in Function Calls
• Whenever a function begins execution an
ACTIVATION RECORD (Stack Frame) is created
• to store the current environment for that function which
includes
This structure should LIFO
because , when a function
terminates, the function with
which to resume execution is
the last function whose
activation record was saved.
Parameters
Caller’s state information
Local variables
Temporary storage
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Stack
Activation Record
Function4
Function3
Function3
Function2
Function2
Function1
Function1
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Palindrome Checking
What is a palindrome?
A palindrome is a word/sentence that is the
same if read both ways.
You might have noticed that if you push some
characters into a stack and pop them out , they
will appear in reverse order.
So Stacks are used for this purpose.
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Palindrome
 Here are some palindromes
MALAYALAM (a south Indian language)
RATS LIVE ON NO EVIL STAR
DAD
POP
RADAR
STEP ON NO PETS
MADAM
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implementation
#include <iostream.h>
#include <string.h>
class ADTstack
{ char stack[10];
int topstack;
public: ADTstack( ) {topstack = -1;};
int empty() {if (topstack == -1) return 1; else return 0;};
int full()
{if (topstack == 9) return 1; else return 0;};
void push(char num) {
if (!full()) { topstack++;
stack[topstack] = num;
}
else cout<<" Stack is Full"<<endl;
}
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implementation
char pop( )
{ char num;
if (!empty())
{
num = stack[topstack];
topstack--; return num;
}
else {cout<<"Stack is Empty"<<endl;
return '0';}
}
};
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implementation
void main()
{
ADTstack st;
char str[10];
int palin, l,i;
cout<<"type in a string to check if it is a palindrome"<<endl;
cin>>str;
l=strlen(str);
if (l==1) {palin=1;} //all strings with 1 character are palindromes
else
{
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implementation
i=0;
while(str[i]!='\0') //push the string into stack
{ st.push(str[i]);
i++;
}
i=0;
while(str[i]!='\0') //pop the string and compare with original
{
if (str[i]!=st.pop()) {palin=0;break;}
i++;
}
}
if (palin==0) cout<<"Not Palindrome"<<endl;
else cout<<"Palindrome"<<endl;
}
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Queue
What is a Queue?
1) It is a data structure for storing some values
2) It is an ADT.
3) Implemented using Arrays or Linked List
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Queue
How to Store and Retrieve from a Queue?
1) A Data Structure in which all Additions to the list are
made at one end, and all Deletions from the list are
made at other end.
2) First item added to a queue (ADD) is always the first
that will be removed (REMOVE) from the queue.
3) This property is called First In First Out also known as
FIFO
4) It can be maintained with two pointers namely FRONT
(REMOVE) and REAR ( ADD).
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Queue
EG - Bank Counter
Front
Rear
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Operations
There are Four operations :
1) Addend ( )
used to add the data at the Tail of the Queue.
Check whether the Queue is full or not
2) Serve ( )
used to remove data at the top of the stack.
Check whether the Queue is empty or not
3) Empty ( )
Checks whether Queue is empty, Tail = -1
4) Full ( )
checks whether Queue is full, Tail = maxqueuesize
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implementation
Uses ARRAY to represent a Queue
Class Queue
{ private :
int Queueelement[4],Head ,Tail;
public:
int Empty( );
Queue( ) { Head =0 ; Tail = -1} int Full ( );
};
void Addend(int);
int Serve( );
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implementation
How to check for full?
Int Queue :: Full( )
{
if (Tail == 3) return 1;
else return 0;
}
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implementation
How to check for Empty?
Int Queue :: Empty( )
{
if (Tail == -1) return 1;
else return 0;
}
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implementation
How to Add?
Void Queue :: Addend(int data2add)
{ if (!Full( ))
{ Tail++;
Queueelement[Tail] = data2add;
}
else
cout << “Queue is Full!!!”<<endl;
}
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implementation
How to Delete?
int Queue :: Serve( )
{int data2remove;
if (!Empty( ))
{ data2remove = Queueelement[0];
for ( i =0;i<Tail;i++)
Queueelement[i] = Queueelement[i+1]
Tail--;
return data2remove; }
else{ cout << “Queue is Empty!!!”<<endl;
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return 0;
}
}
implementation
Void main( )
{
Queue queueobj;
queueobj.Addend(23);
queueobj.Addend(46);
queueobj.Addend(37);
queueobj.Addend(10);
queueobj.Addend(55);
cout << queueobj.Serve();
cout << queueobj.Serve();
}
23
46
23
37
46
10
55
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Serving
Three Methods of Serving
1) increment head to 1
runs out of storage
2) when the first person has be served the remaining persons in the
Queue shuffle forward one place.
Can serve unlimited number of persons as long as the queue never
exceeds the maximum size
3) Use cyclic queues
One of the application of Queues is simulation
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• Cyclic Queues
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Cyclic Queues
What is a Cyclic Queue?
we need to imagine that the array allocated to the queue
is not linear but cyclic, i.e. that it forms a circle.
EG:
So that if for instance 10 elements are allocated to the queue with
the element positions running from 0 to 9 then when the tail gets
to position 9 the next element to be added can go to position 0
providing that position has already been “served” (vacant).
.Thus the two problems of the queues are solved .
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Cyclic Queue
Example: Queue implemented using an array of size 6 with 4 data items
inserted in to the queue
Head
Tail
0 1 2 3 4 5
The following actions will cause the “head” and “tail” to
move through the array as listed below:
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Cyclic Queue
Action
Delete
Insert
Delete
Insert
Insert
Delete
Delete
Head
0
1
1
2
2
2
3
4
Tail
3
3
4
4 Head
5
0
0
0
0 1
Tail
2
3
436 5
Cyclic Queue
Action
Insert
Delete
Insert
Delete
Head
4
5
5
0
Tail
1
Head
1
2
2
Tail
0 1 2 3 4 5
Note: A Cyclic queue will always be of fixed size (say n)
and the size information must be available to update
the pointers “head” and “tail”.
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Cyclic Queue
The wrapping around can be achieved by updating the
pointers as follows:
Delete: head = (head+1) % n
Insert: tail = (tail + 1) % n
i.e., Whenever a pointer is incremented, take modulo n.
The above operations is needed to check if the queue is
empty or full.
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Cyclic Queue
Consider when there is only one element in the queue
• In this case, both the pointers coincide (head == tail)
• The queue becomes empty when the element is deleted
Head ,Tail
Tail
Head
0
1
2
3 4 5
Only one element Queue
0
1 2 3 4 5
Empty Queue
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Cyclic Queue
For an empty queue, we have the condition
head = (tail + 1) % n
The above condition is also satisfied when the queue is full
We resolve the ambiguity between two cases
if the condition head = (tail+1)% n is satisfied up on deleting an
item from the queue, then queue is empty
if the condition head = (tail + 1) % n is satisfied up on inserting an
item in to the queue, then queue is full.
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implementation
How to Add?
void Addend(int x)
{
if (!Full())
{
tail=(tail+1)%MAX;
a[tail]=x;
count++;
cout<<x<<" added to the queue"<<endl;
}
else cout<<"Full Queue"<<endl;
}
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implementation
How to Delete?
int Serve()
{ int x;
if (!Empty())
{
x=a[head];
head=(head+1)%MAX;
count--;
cout<<x<<" served from the queue"<<endl;
return x;
}
else cout<<"Empty Queue"<<endl;
}
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