c-stacks & queues

8/8/2019 C-Stacks & Queues

1/22

27-03-03 P.P.Chakrabarti, IIT Kharagpur1

Dynamic 2D arrays,Stacks, Queues

P. P. Chakrabarti


2/22


2D Arrays using arrays of pointers

#define N 20

#define M 10

main()

{ char word[N], *w[M];

int i, n;

scanf("%d",&n);

for (i=0; i


3/22


w

0

1

2

3

9

How it will look like

\0rakludneT

\0varuoS

\0nahK

\0aidnI


4/22


2D Arrays using a pointer to a pointer

#define N 20

main(){

char word[N], **w; /* **w is a pointer to a pointer array */

int i, n;

scanf("%d",&n);

w = (char **) malloc (n * sizeof(char *));

for (i=0; i


5/22


w

0

1

2

3

4

How this will look like

\0aidnI

\0aknaLirS

\0ailartsuA

\0ayneK

N \0dnalaeZwe


6/22


2D Array of n rows and constant columns:Single pointer + memory chunk

int (*r)[COLS], rows,

scanf("%d",&rows);

r = (int (*)[COLS])malloc(rows*COLS*sizeof(int));

r

Dynamically allocated memory

r[0][0]


7/22


2D Arrays of n rows and 3 columns

#define COLS 3

main()

{ int (*r)[COLS], rows, i,j;

scanf("%d",&rows);

r = (int (*)[COLS])malloc(rows*COLS*sizeof(int));

for (i=0;i


8/22


The Stack ADTPush

Pop

A Stack is a Last-in-First-Out (LIFO) list with all

or some of the following interface functions:

create: makes a new stack (of a given size)

dispose: destroys a stack

make_empty: makes the stack empty

push: inserts an element into the stack

pop: removes the top element from the stack

isempty: determines if the stack has no elements

isfull: determines if the stack is full in case of abounded sized stack

push is like inserting at the front of the list

pop is like deleting from the front of the list


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Postfix Evaluation

Input format: [code, value] sequence

Example: 12*4+3 is coded in postfix in the formofab*c+ as 0 12 0 4 1 2 0 3 1 0 2

For evaluation, we define a stack of element-type(say integers/float, etc).

The overall algorithm is as follows:

(a) Read next input;

(b) If input is end then top of stack containsresult;

(c) If input is operand, push value into stack;

(d) If Input is operator, pop out (remove) thetop two elements from the stack, performthe operation and push the resultant valueinto the stack;

End2

Operator1

Operand0

MeaningCode

/3

*2

-1

+0

OperationOp-code


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Postfix Evaluation: Example 1

(12*4)+3 == 12,4,*,3,+

Input: 0 12 0 4 1 2 0 3 1 0 2

End2

Operator1

Operand0

MeaningCode

/3

*2

-1

+0

OperationOp-code

12 12

4

48 48

3

51


11/22


Postfix Evaluation: Example 2

2+4*5+3*2 == 2,4,5,*,+,3,2,*,+

2 2

4

2

4

5

2

20

22 22

3

22

3

2

22

6

28


12/22


fib (5)

fib (3) fib (4)

fib (1)

fib (2)fib (1) fib (2)

fib (0)

fib (3)

fib (1)

fib (1) fib (2)

fib (0)

fib (0) fib (1)

Fibonacci recurrence:

fib(n) = 1 if n =0 or 1;

= fib(n 2) + fib(n 1)otherwise;

Recursion can beimplemented as a stack


13/22


Fibonacci recursion stack

5 4

3

4

21

4

2

4

10

4

1

4 3

2

3

10

0 0 0 1 1 2 3 3 3

31

3 21

2 10

1

4 5 5 6 6 7 8


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Tower of Hanoi

A B C


15/22


Tower of Hanoi

A B C


16/22


Tower of Hanoi

A B C


17/22


Tower of Hanoi

A B C


18/22


Towers of Hanoi function

void towers (int n , char from, char to, char aux){/ * Base Condition */

if (n==1) {printf (Disk 1 : % c -> % c \ n, from, to) ;return ;

}/ * Recursive Condition */

tow ers (n-1, from, aux, to) ;

printf (Disk % d : % c -> % c\ n, n, from, to) ;tow ers (n-1, aux , to, from) ;

}


19/22


TOH recursion stack

3,A,B,C 2,C,B,A

A to B

2,A,C,B

1,A,B,C

2,C,B,A

A to B

1,B,C,A

A to CA to B

2,C,B,A

A to B

1,B,C,A

A to C

2,C,B,A

A to B

1,B,C,A

A to C

2,C,B,A

A to B

1,B,C,A

2,C,B,A

A to B

B to C

2,C,B,A

A to B

2,C,B,A 1,A,B,C

C to B

1,C,A,B


20/22


The Queue ADTEnqueue

Dequeue

A Stack is a First-in-First-Out (FIFO) list with thefollowing interface functions:

create: makes a new queue of a given size in case

of a bounded queue

dispose: destroys a queue make_empty: makes queue empty

enqueue: inserts an element at the rear

dequeue: removes the element in front

isempty: determines if the queue has no elements isfull: determines if the queue is full in case of a

bounded sized stack

REAR

FRONT


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Possible Implementations

Linear Arrays:(static/dynamicaly allocated)

front rear

Circular Arrays:(static/dynamicaly allocated)

Can be implemented by a one-D

array using modulus operations.

frontrear

Linked Lists: Use a linear

linked list with insert_rear

and delete_front operations


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Exercises Implement the Queue as an array. (Read

the concept of a circular queue). Writedown the data definition and all theinterface functions.

Implement the Queue as a linked list. Implement a Priority Queue which

maintains the items in an order (ascending/

descending) and has additional functionslike remove_max and remove_min.

Maintain a Doctors appointment list

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