stack details....in c++

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Data Structures

Dr Kazi A KalpomaAssociate Professor

Faculty of Science and Information Technology

American International University Bangladesh (AIUB)

Contact: [email protected]

DS Lecture 06Stack

3/9/2014 Dr. Kazi A. Kalpoma 1
mailto:[email protected]:[email protected]


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3

A stack is open at one end

(the top) only. You can push

entry onto the top, or popthe top entry out of the stack.

Note that you cannot

add/extract entry in the

middle of the stack.

Stack

A

B

C

bottom

top

pushpop


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Last-in First-out (LIFO)

A A

B

A

B

C

When we push entries

onto the stack and thenpop them out one by one,

we will get the entries in

reverse order.

The last one

pushed in is the

first one poppedout! (LIFO)

A A

B

Insert(A);

Insert(B);

Insert(C);

Remove();

Remove();

Remove();


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Stack Operations

Push(X) insert X as the topelement of the stack

Pop()remove the top element ofthe stack and return it.

Top()return the top element

without removing it from the stack.


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Stack Operations

push(2)

top 2

push(5)

top

2

5

push(7)

top

2

5

7

push(1)

top

2

5

7

1

1 pop()

top

2

57

push(21)

top

2

57

21

21 pop()

top

2

57

7 pop()

2

5top

5 pop()

2top

top


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Stack using an Array

top

2

5

7

12 5 7 1

0 1 32 4

top = 3


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#define stack_size 6;

int top;

char stack[stack_size];

Array implementation

A

B

?

?

?

?

top = 2

stack

stack


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Initialization of Stack

stack_initialize()

{

top = -1;

}

?

?

?

?

?

?

top = 0

entrytop


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Push()

void push(char i)

{

if(top==stack_size - 1)

cout


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Pop()void pop()

{if(top


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Traversing a stack

void show()

{

int i;for(i=0;i


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Other operations

int top(){

return stack[top];}

int IsEmpty(){

return ( top == -1 );}

int IsFull(){return ( top == stack_size-1);

}


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Example of PUSH() and POP()

3/9/2014 Dr. Kazi A. Kalpoma 14

top0

1

2

3

stack

void main()

{

push(7);

push (8);

push (9);pop ( );

push (5);

pop ( );

pop ( );

}

4

5

stack[0]=7 and top = 0


stack[2]=9 and top = 2x = 9 and top = 1


x = 5 and top = 1

x = 8 and top = 0


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Stack Using Linked List

We can avoid the size limitation of a stackimplemented with an array by using a linked

list to hold the stack elements.


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Stack Using Linked List

For a singly-linked list, insert at startor endtakes constant time using the headand currentpointers respectively.

Removing an element at the startis constanttime but removal at the endrequired traversingthe list to the node one before the last.

Make sense to place stack elements at the start

of the list because insert and removal areconstant time.


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Stack Operation: List

int pop(){

int x = head->data;

Node* p = head;

head = head->Next;

delete p;

return x;}

top

2

5

7 1 7 5 2

head


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void push(int x){

Node* newNode = new Node();

newNode->data = x;

newNode->Next = head;

head = newNode;}

top

2

5

7

9

7 5 2

head

push(9)

9

newNode


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int top(){

return head->data;}

int IsEmpty(){

return ( head == NULL );}

IsFull()is not needed anymore.


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Stack: Array or List

Since both implementations support stackoperations in constant time, any reason to chooseone over the other?

Allocating and de-allocating memory for list nodes

does take more time than pre-allocated array.

List uses only as much memory as required by thenodes; array requires allocation ahead of time.

List pointers (head, next) require extra memory.

Array has an upper limit; List is limited by dynamicmemory allocation.

stack details....in c++

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