lecture11 of dsf

8/7/2019 lecture11 of dsf

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Stacks and queues


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stack

A stack is theordered list inwhich all insertionand deletion willbe done at thesingle end.

Typical example of

stack is stack ofplates

60

50

40

3020

10

top


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Primitive stack operations

To create a stack

To insert one element

To delete one element

To check which element is onto top

To check whether the stack empty

or not.


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Stack using array

#include #include #include #define size 5

struct stack { int s[size]; int top; }st;


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Stack using array

int stfull()

{

if(st.top>=size-1)

return 1;

else

return 0;

}


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void push(int item) { st.top++; st.s[st.top]=item; } int stempty() { if(st.top==-1) return 1; else return 0; }


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int pop()

{

int item; item=st.s[st.top];

st.top--;

return(item); }


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void display()

{

int i;

if(stempty()) printf("\n Stack is empty!!");

else

{

for(i=st.top;i>=0;i--)

printf("\n%d",st.s[i]); }

}


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void main(void) { int item,choice; char ans;

st.top=-1; clrscr(); printf("\n\t\t Implementation of stack"); do { printf("\n Main menu"); printf("\n1.Push\n2.Pop\n3.Display\n4.Exit"); printf("\nEnter your choice: "); scanf("%d",&choice);


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switch(choice) { case 1:printf("\nEnter the item to be

pushed: "); scanf("%d",&item); if(stfull()) printf("\nStack is full!"); else push(item); break;


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case 2:if(stempty())

printf("\nEmptyStack!Underflow!!");

else

{

item=pop();

printf("\nThe popped element

is: %d",item); }

break;


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case 3:display(); break; case 4: exit(0);

} printf("\nDo you want to continue?"); ans=getche(); }

while(ans=='Y'||ans=='y'); getch(); }


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STACK USING LINK LIST

#include

#include

#include #include

typedef struct stack{ int data;

structstack*next;}node;


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void main() { node*top; int val,item,choice; char ans,ch; void push(int ,node**); void display(node**); int pop(node**); int sempty(node*); clrscr(); top=NULL; printf("\nstack using linklist");


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do { printf("\n1.push\n2.pop\n3.display\n4.exit"); printf("\nenter ur choice");

scanf("%d",&choice); switch(choice) { case 1:printf("\nenter the data"); scanf("%d",&val);

push(v

al,&top); break; case 2:if (sempty(top)) printf("\nstack is empty");


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else { item=pop(&top); printf("\npopped elementis%d",item); } break; case 3:display(&top); break; case 4:printf("do u want 2 quit"); ch=getche(); if(ch=='y') exit(0); else break;


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default:printf("\nwrong choice");

}

printf("\ndo u want2 continue");

ans=getche();

}

while(ans=='y');

getch();

}


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void push(int item,node**top)

{

node*New; node*get_node(int);

New=get_node(item);

New->next=*top;

*top=New;

}


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node*get_node(int item) { node*temp;

temp=(node*)malloc(sizeof(node)); if(temp==NULL) printf("\n memory is not allocated"); temp->data=item;

temp->next=NULL; return temp; }


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int sempty(node*temp)

{

if(temp==NULL) return 1;

else

return 0; }


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int pop(node**top) { int item;

node*temp; item=(*top) ->data; temp=(*top); *top=(*top) ->next;

free(temp); return (item); }


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void display(node**head)

{

node*temp; temp=*head;

if(sempty(temp))

printf("\nstack is empty");


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else

{

while(temp!=NULL)

{ printf("%d",temp->data);

temp=temp->next;

}

} getch();

}


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Application of stack

Various application of the stack

Expression conversion

Expression evaluation Parsing well formed parenthesis

Decimal to binary conversion

Reversing a string Storing function call


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Concept ofinfix prefix and postfix

expression

Expression is the combination of theoperand and operator operand are

numaricvalue and operator are oftwo type

Unary + and

Binary +,-,*,/ and exponential in

general

Three types of expression


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Concept ofinfix prefix and postfix

expression

Infix expression (operand1 operatoroperand2)

A+B

(a+b)*(c-d) (a+b/e)*(d+f)

PostfixExpression(operand1operand2opewrator)

ab+ ab+cd-*

ab+e/df+*


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Prefix Expression

Prefix=operatoroperand1operand2

+ab

*+ab-cd */+abe+df


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Conversion of infix to postfix

expression

Algorithm

Read the infix expression for left to rightone character at a time

Initially push $ onto the stack for $instack set priority as -1 if input symbolread is( then push it on to the stack

If the input symbol read is an opersndthen place it in postfix expression

If the input symbol read is operator


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a)Check if priority of operator in stack is greaterthan the priority of incoming operator then popthe operator from the stack and place itin thepostfix expression.repeat step 4 a) till we get the

opertator from the stack which has greaterpriority then incoming operator.

b)otherwise push the operator being read ontothe stack

C) if we read input operator as the ) then pop the

operator until we not get (

Final pop all th content until stack becomesempty append them to postfix expression.


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operator Instackpriorities

Incomingpriorities

+or- 2 1

*or/ 4 3

^ for anyexponential

5 6

( 0 9

Operand 8 7

) na 0


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Program for Evaluation of postfix

expression

Algorithm

Read the post fix expression from left toright

If input symbol as operand push it ontothe stack

If operator is read pop two operand andperform arithmatic operation

Push the result onto the stack Repeat steps 1-4 until postfix expression

not over,


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program

#include #include #include

#define size 80

struct stack {

double s[size]; int top; }st;


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void main() { char exp[size];

int len; Double result; Double post(); clrscr();

printf("\nEnter a postfix expression :");


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scanf(%s, &exp);

len=strlen(exp);

exp[len]=$; result=post[exp];

Printf(\n the value of theexpression is%f,result);

getch(); }


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double post(char exp[]) { char ch, *type; Double result ,val,op1,op2;

Void push (double);

Double pop(); int i; St.top=-1; i=0; Ch=exp[i];

While(ch!=$) {


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if(ch>=0&& ch


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Else if(strcmp(type,operator)==0) { op2=pop();

op1=pop();

switch(ch) { case '+': result=op1+op2; break; case '-:result=op1-op2; break;


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case '*':result=op1*op2;

break;

case'/':result=op1/op2;break;

case^':result=pow(op1,op2);break


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}

Push(result);

}

i++;

Ch=exp[i];

}

Result=pop();

Return result;

}


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Void push(double val)

{

If (st.top>=size-1) Printf(\n stack full);

St.top++;

St.s[st.top]=val; }


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Double pop()

{

Double val;

If(st.top==-1)

Printf(\n stack is empty);

Val=st.s[st.top];

St.top--;

Return val;

}


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queues

The queue is defined as theordered collection of elements that

has two ends front and rear fromthe front end one can remove theelement and from the rear end onecan delet the element.

Ex people waiting for ticket counter.


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Operation on queue

The queue is called as FIFO,

Operations like

Queue overflow

Insertion of the element into thequeue

Queue underflow

Deletion of the element Display of the queue


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Operation on queue

Before performing the insert operation we check thequeue overflow

Before performing the deletion we check the queueis underflow

10 20 30 40 50 60

Rear end

Frontend


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queue using array

#include

#include

#include

#define size 5

struct Queue

{

int que[size];

int front,rear;

}Q;


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Int Qfull()

{

if(Q.rear>=size-1) return 1;

else

return 0; }


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int insert(int item)

{

if(Q.front==-1) Q.front++;

Q.que[++Q.rear]=item;

return Q.rear; }


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int Qempty()

{

if((Q.front==-1)||(Q.front>Q.rear)) return 1;

else

return 0; }


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void display()

{

int i; printf("\nThe elements are:- \n");

for(i=Q.front;i


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void main()

{

int choice,item;

char ans; clrscr();

Q.front=-1;

Q.rear=-1;

do {


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printf("\nQUEUE is FULL");

else

{

printf("\nEnter the element tobe inserted:- ");

scanf("%d",&item);

insert(item); }

break;


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case 2:if(Qempty()) printf("\nQUEUE is EMPTY"); else

item=delet(); break; case 3:if(Qempty()) printf("\nQUEUE is EMPTY"); else display(); break;


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void main(void)

{

char ans;

int ch; void insert();

Q *delet();

void display(Q *);

front=NULL;

rear=NULL; do

{


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printf("\n\tProgram for queue using link list\n");

printf("\nMain Menu");

printf("\n1.Insert\n2.Delete\n3.Display");

printf("\nEnter Your Choice"); scanf("%d",&ch);

switch(ch)

{

case 1:insert();

break; case 2:front=delet();


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while(ans=='y'||ans=='Y'); getch(); clrscr();

} Q *get_node(Q *temp) { temp=(Q *)malloc(sizeof(Q)); temp->next=NULL; return temp; }


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void insert() { char ch; Q *temp; temp=get_node(temp); printf("\nInsert the elelment in the queue:\n"); scanf("%d",&temp->data); if(front==NULL) {

front=temp; rear=temp; }


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else {

rear->next=temp;

rear=rear->next;

}

} int Qempty(Q *front)

{

if(front==NULL)

return 1;

else

return 0;

}


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else { printf("\n\tThe deleted Element is

%d",temp->data); front=front->next; temp->next=NULL; free(temp); } return front; }


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lecture11 of dsf

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