ds l8 stack&queue

8/8/2019 DS L8 Stack&Queue

1/23

Data Structure

Stacks and Queues


2/23

Introduction to Stack

An stack is a ordered list in which insertion and deletions

are made at one end.

The location of stack end is stored in a variable

called top.

Given a stack S=(a0, a1, , an-1), we say a0 is the

bottom element, an-1 is the top element.


3/23

Stack

Last-In-First-Out (LIFO)

Add (A)

Add (B)

Add (C)

Add (D)

Add (E)

Pop ()

Which one is popped by the function Pop()?

A

B

C

D

E

Add a new item on the top of stack.

Get the item at the top of stack and

remove it from the stack.top

0

1

2

3

4

5


4/23

Examples of Stack

Stack

0 1 2 3 4

0

1

2

3

4

(0, 0)

(0, 1)

(1, 1)

(1, 0)

(2, 0)

(2, 1)

(3, 1)

(3, 0)(4, 0)

(4, 1)

(3, 2)


5/23

System Stack

System stack is used by a program at runtime to process

function calls.

Whenever a function is invoked, the program create a

structure referred to as an activation recordorstack

frame.


6/23

System Stack

- Frame pointer (fp): a pointer to current stack frame.

- Placed on top of the system stack

Previous frame pointer:

- a pointer to the previous stack frame of the invoking

function.

Return address:

- The location of the statement to be executed after the

function

terminates.


7/23

System Stack

local varaibles

return address

previous frame pointer

main:

al:

fp

return address


return address

void al()

{

return;

}

int main ()

{

al();

return 0;

}


return address


8/23

The Stack ADT

class Stack

{

public:

Stack(int=10);~ Stack();

void ush(int d);

int Pop();

//Check if the stack is emptybool IsEmpty();

};


9/23

Implementing Stack Using Array

class Stack

{

private:Resize();

int top, capacity;

int *stackarray;};


10/23

Constructor for Stack

The variable top indicate next element to be popped.

- Initially, top is assigned -1.

Stack::Stack(int s)

{

capacity= s;

top = -1;allocate memory space of size s forstackarray;

}


11/23

Push() and Pop()

Pop

- Immediately return the value at the top.

For example:

int d= stackarray[top];

top--;

return d;

Before returning the value, first check if the stack is empty.If so, throw an exception.


12/23

Push() and Pop()

Push:

Note that if the stack is full, invoke Resize() to enlarge the

capacity of array

Since top indicates the element to be popped, you mustincrease top by 1 first when pushing a new element.

void Stack::Push(int num)

{

if (top+1 >= capacity)Resize();

top++;

stackarray[top] = num;

}


13/23

How to Resize the Array?

void Stack::Resize()

{

newsize = capacity* 2;

Allocate a new array of size newsize;

Copy elements from stackarrayto the new array;

deallocate stackarray;

assign the pointer of the new array to stackarray;

capacity= newsize;

}


14/23

Output Stack Elements

A

B

C

D

E

E D C B A

The order is reversed and the stack becomes empty!

E

D

C

B

A

Buffer

EDCBA


15/23

The Queue ADT

class Queue

{

public:

Queue (int=10);

~ Queue();

void Push(int d);

int Pop();

//Check if the queue is empty

bool IsEmpty();

bool IsFull();

};


16/23

Queue

First-In-First-Out (FIFO)

Push (A)

Push (B)

Push (C)

Push (D)

Push (E)

Pop ()A

B

C

D

E

rearfront


17/23

Implementation Using Array

Suppose the length of array is n.

This approach runs into a problem when rear equals

to n-1.

Shifting all elements to the left could take O(n) time.

A A B A B C

rear rear rear

B C

rearfront

B C D

rearfront

front


18/23

Circular Queue

A

B C

D

0 1 2 3 4 5 6 7

A B C D

0

1

2 3

4

5

67

rear

front

rear

rear rear

front

front (1)

Push (A)

Push (B)

Push (C)

Push (D)

Pop ()Pop ()

Pop ()

Push (E)

Push (F)Push (G)

Push (H)

Push (I)

rear

rear

frontfront

E

FG

H

I

E

rear

F

rear

G

rear

H I


19/23

Implementing Circular Queue

class Queue

{

private:Resize();

int front, rear;

int top, capacity;

int *queuearray;

};


20/23

Constructor for Circular Queue

Initially, rearand frontare assigned 0.

(rear+1) indicates the next location to insert; (front+1)

indicates the next location to insert.

This gives a situation to determine if the queue is empty.

Queue is empty: rear == front


21/23


0

1

2 3

4

5

67

rear

front

0

1

2 3

4

5

67

front

rear

A

B C

D

E

FGrear

H

How do know whether the queue is

empty or full?


22/23


Queue:: Queue(int s)

{

capacity= s;

front= rear= 0;allocate memory space of size s forqueuearray;

}


23/23

IsEmpty() and Pop()

Before returning the value, first check if

the queue is empty.

bool Queue:: IsEmpty(){

if (front== rear)

return true;

return false;

}

ds l8 stack&queue

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