# LINKED LIST, STACKS AND QUEUES Saras M Srivastava, PGT – Comp. Sc. Kendriya Vidyalaya TengaValley.

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LINKED LIST, STACKS AND QUEUES Saras M Srivastava, PGT – Comp. Sc. Kendriya Vidyalaya TengaValley

LINKED LIST Singly Linked List: Contains the address of the next node. Doubly Linked List: Contains the address of the next node as well as address of previous nodes also. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 2

OPERATIONS TO BE PERFORMED IN LINKED LIST Insertion of Node In the beginning At the End of the Linked List Deletion of the Node Traversal of the Linked List SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 3

INSERTION OF THE NODE ( IN THE BEGINNING) Algorithm 1.Ptr = start 2.newptr = new node 3.If newptr = NULL 4.Print No Space Available (Overflow)! Exiting 5.Else 6.{ newptr -> data = item 7.Newptr -> next = NULL SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 4

8. if start = NULL then 9. start = newptr 10. else { 11. save = start 12. start = newptr 13. newptr -> next = save 14. } } 15. End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 5

IMPLEMENTATION OF THE ALGORITHM IN PROGRAM #include struct node { int info; node *next; } *start,*newptr,*ptr,*save; SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 6 node* create_new_node( int n ) { ptr=new node; ptr->info=n; ptr->next=NULL; return ptr; }

void insert_beg (node* np) { if(start==NULL) start=np; else { save=start; start=np; np-> next=save; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 7 void display(node* np) { while (np!=NULL) { cout info "; np=np->next ; } cout >>>>!!!!!!"; }

void main() { start= NULL; int inf ; char ch='y'; while(ch=='y' || ch=='Y') { clrscr(); cout<<"\n enter information of the new node.."; cin>>inf ; cout<<"\n creating new node ! ! press enter to continue..."; getch(); SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 8 newptr = creat_new_node(inf); if( newptr!= NULL) { cout<<"\n \n new code created successfully. press enter to cointinue.."; getch(); } else { cout<<"\n cannot create new code \t "; exit(1); }

cout<<"\n \t now inserting this node in the beginning of the list "; cout<<"\n \t press enter continue "; getch(); insert_beg(newptr); cout<<"\n now the list is: \n"; display(start); cout<<"\n \a \t press enter y to enter new node, n to exit: " ; cin>>ch; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 9

INSERTION OF THE NODE ( AT THE END) Algorithm 1.Ptr = start 2.newptr = new node 3.If newptr = NULL 4.Print No Space Available (Overflow)! Exiting 5.Else 6.{ newptr -> data = item 7.newptr -> next = NULL SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 10

8. if start = NULL then { 9. start = newptr 10. rear = newptr } 8. else { 9. rear -> next = newptr 10. rear = newptr } 8. End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 11

IMPLEMENTATION OF THE ALGORITHM IN PROGRAM #include struct node { int info; node *next; } *start,*newptr,*ptr,*save, *rear; SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 12 node* creat_new_node( int n ) { ptr=new node; ptr->info=n; ptr->next=NULL; return ptr; }

void insert_End (node* np) { if(start==NULL) { start=np; rear = np; } else { rear -> next = np; rear = np; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 13 void display(node* np) { while (np!=NULL) { cout info "; np=np->next ; } cout >>>>!!!!!!"; }

void main() { start= rear = NULL; int inf ; char ch='y'; while(ch=='y' || ch=='Y') { clrscr(); cout<<"\n enter information of the new node.."; cin>>inf ; cout<<"\n creating new node ! ! press enter to continue..."; getch(); SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 14 newptr = creat_new_node(inf); if( newptr!= NULL) { cout<<"\n \n new code created successfully. press enter to continue.."; getch(); } else { cout<<"\n cannot create new code \t "; exit(1); }

cout<<"\n \t now inserting this node at the end of the list "; cout<<"\n \t press enter continue "; getch(); insert_end(newptr); cout<<"\n now the list is: \n"; display(start); cout<<"\n \a \t press enter y to enter new node, n to exit: " ; cin>>ch; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 15

DELETION OF THE NODE FROM THE BEGINNING Algorithm 1.If start = NULL then 2.Print Underflow 3.Else { 4.Ptr = start 5.Start = start ->next 6.Delete ptr } 7.End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 16

IMPLEMENTATION OF THE ALGORITHM IN PROGRAM void DelNode( ) { if (start == NULL) cout << \n Underflow!!!!!; else { ptr = start; start = start ->next; delete ptr; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 17

STACK A LIFO Structure Can be implemented as an array or as a linked list. Operations in Stack: Push (Addition of Elements) Pop (Removal / Deletion on elements) SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 18

STACK AS AN ARRAY (POP) Algorithm 1.If top < -1 then 2.print underflow !!!!!!! Aborting 3.Else { 4.Data = stack [top] 5.Top = top -1 } 6.End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 19

STACK AS AN ARRAY (PUSH) Algorithm 1.Top = - 1 2.Read item 3.If top == (size – 1) then 4.Print No Space Available (Overflow)! Exiting 5.Else 6.{ top = top + 1 7.Stack[top] = item } 8.End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 20

#include const int sz = 50; void push(int stack[], int &top, int ele) { if(top == (sz - 1)) { cout << "\n Stack overflow"; exit(1); } else { top ++; stack[top = ele; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 21

void pop(int stack[], int &top){ if(top < 0) { cout << "\n Underflow"; exit(1); } else cout << "\n Poped Element: " << stack[top--]; } void Display(int stack[], int top) { if(top == -1) return; for( int i = top; i >= 0; i--) cout << stack[i] <<endl; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 22

void main(){ int stack[sz], item, top = -1, res; char ch = 'y'; clrscr(); while(ch == 'y' || ch == 'Y'){ cout << "\n Enter item for insertion: "; cin >> item; push(stack, top, item); cout << "\n Do you want to enter more elements (y/n) : "; cin >> ch; } cout << "\n The stack now is: "; Display(stack, top); SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 23

cout << "\n Do you want to delete elements (y/n) : "; cin >> ch; while(ch == 'y' || ch == 'Y'){ pop(stack,top); cout << "\n Do you want to enter more elements (y/n) : "; cin >> ch; } cout << "\n The stack now is: "; Display(stack, top); } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 24

STACK AS A LINKED LIST (PUSH) Algorithm 1.Newptr = new Node 2.Newptr -> info = item; Newptr -> next = NULL 3.If top == NULL ) then 4.top = Newptr 5.Else 6.{ Newptr -> next = top 7.top = Newptr } 8.End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 25

STACK AS A LINKED LIST (POP) Algorithm 1.If top == NULL then 2.Print Stack is Empty (Underflow), Exit 3.Else { 4.Print Top -> info 5.Top = top -> next } 6.End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 26

IMPLEMENTATION OF THE ALGORITHM IN PROGRAM #include struct node { int info; node *next; } *top,*newptr,*ptr,*save; SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 27 node* creat_new_node( int n ) { ptr=new node; ptr->info=n; ptr->next=NULL; return ptr; }

void Push (node* np) { if(top==NULL) top = np; else { save = top; top = np; np-> next = save; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 28 void display(node* np) { while (np != NULL) { cout info "; np = np->next ; } cout >>>>!!!!!!"; }

void Pop( ) { if (top == NULL) { cout << \n Underflow!!!!!; exit(1); } else { ptr = top; top = top ->next; delete ptr; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 29

void main() { top = NULL; int inf ; char ch='y'; while(ch=='y' || ch=='Y') { clrscr(); cout<<"\n enter information of the new node.."; cin >> inf ; cout<<"\n creating new node ! ! press enter to continue..."; getch(); SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 30 newptr = creat_new_node(inf); if( newptr != NULL) { cout<<"\n \n new code created successfully. press enter to continue.."; getch(); } else { cout<<"\n cannot create new code \t "; exit(1); }

cout<<"\n \t now Pushing this node into the stack "; cout<<"\n \t press enter continue "; getch(); Push(newptr); cout<<"\n now the Stack is: \n"; display(top); cout<<"\n \a \t press y to enter new node, n to exit: " ; cin>>ch; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 31

APPLICATIONS OF STACK Reversing a String Polish String Conversion of Infix Expression to Postfix Expression Evaluation of Postfix Expression Processing of Function (Subprogram) Calls Matching Parenthesis SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 32

Infix Notation Operators placed between two operands. E.g. A + B, A – B, A * B, A / B, A ^ B etc Postfix Notation (Reverse Polish Notation) Operators placed after two operands. E.g. AB +, AB -, AB * etc. Prefix Notation (Polish Notation) Operators placed before two operands. E.g. + AB, - AB, * AB etc. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 33 The Name Polish Notation and Reverse Polish Notation are named after Polish Logician Jan Lukasiewiez

CONVERSION FROM INFIX TO POST FIX (ALGORITHM) 1.Enclose the exp in Parenthesis i.e. ( ) 2.Read Next symbol of the exp and repeat steps 3 to 6 until the stack is empty and go to step 7 3.If symbol read = operand then add it to Postfix Exp. 4.If symbol read = ( then push it into the stack 5.If the symbol read = operator then 1.Repeat while ( Priority of Top(stack) >= Priority of operator ) 1.{pop operator from stack 2. Add Operator to Postfix Expression } 2.Push Operator into Stack 6.if the Symbol read = ) then 1.Repeat while ( Top(stack) != ( ) 1.{pop operator from stack 2. Add Operator to Postfix Expression } 2.Remove the (, It must not be added to Postfix Expression 7.End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 34

EVALUATION OF POSTFIX EXPRESSION: 1.START 2.Read the element 3.If element = operand then Push the element into stack 4.If element = operator then Pop two operands from stack (One operand in case of NOT Operator) Evaluate the expression formed by two operands and the operator. Push the result of expression into stack 5.If no more elements then Pop the result 6.Else Goto step 2 7.END SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 35

QUEUE SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 36

THE QUEUE OPERATIONS A queue is like a line of people waiting for a bank teller. The queue has a front and a rear. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 37 \$ Front Rear

THE QUEUE OPERATIONS New people must enter the queue at the rear. The C++ queue class calls this a push, although it is usually called an enqueue operation. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 38 \$ Front Rear

THE QUEUE OPERATIONS When an item is taken from the queue, it always comes from the front. The C++ queue calls this a pop, although it is usually called a dequeue operation. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 39 \$ Front Rear

ARRAY IMPLEMENTATION A queue can be implemented with an array, as shown here. For example, this queue contains the integers 4 (at the front), 8 and 6 (at the rear). SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 40 [ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ]... An array of integers to implement a queue of integers 486 We don't care what's in this part of the array.

ARRAY IMPLEMENTATION The easiest implementation also keeps track of the number of items in the queue and the index of the first element (at the front of the queue), the last element (at the rear). SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 41 [ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ]... 486 size 3 first 0 last 2

A DEQUEUE OPERATION When an element leaves the queue, size is decremented, and first changes, too. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 42 [ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ]... 486 size 2 first 1 last 2

AN ENQUEUE OPERATION When an element enters the queue, size is incremented, and last changes, too. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 43 [ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ]... 2 86 size 3 first 1 last 3

AT THE END OF THE ARRAY There is special behavior at the end of the array. For example, suppose we want to add a new element to this queue, where the last index is [5]: SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 44 [ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ] 216 size 3 first 3 last 5

AT THE END OF THE ARRAY The new element goes at the front of the array (if that spot isnt already used): SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 45 [ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ] 216 size 4 first 3 last 0 4

ARRAY IMPLEMENTATION Easy to implement But it has a limited capacity with a fixed array Or you must use a dynamic array for an unbounded capacity Special behavior is needed when the rear reaches the end of the array. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 46 [ 0 ] [1] [ 2 ] [ 3 ] [ 4 ] [ 5 ]... 486 size 3 first 0 last 2

INSERTION IN THE QUEUE : Algorithm 1.Start 2.If rear = null (-1) then { 3.Rear = Front = 0 4.Queue [0] = item } 5.Else if Rear = N – 1 then 6. Print OVERFLOW 7.Else 8. Queue [Rear ++ ] = item 9.END SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 47

DELETION IN THE QUEUE: Algorithm Start If Front = null (-1) then Print UNDERFLOW Else { Item = Queue [Front] If Front = Rear Then Front = Rear = 0 } Else Front ++ END SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 48

#include int insert_in_Q(int[],int); void display(int[],int,int); const int size = 50; int Q[size], front=-1, rear=-1; SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 49 Implementation of the Algorithm in Program: int insert_in_Q(int Q[ ], int ele) { if (rear==size-1) return -1; else if (rear==-1) { front = rear = 0 ; Q[rear]=ele; } else { rear++; Q[rear]=ele; } return 0; }

int remove(int Q[ ]) { int ret; if(front == -1) return -1 ; else { ret = Q[front]; if(front==rear) front=rear=-1; else front++; } return ret; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 50 Implementation of the Algorithm in Program: void display (int Q[ ],int front,int rear) { if( front == -1) return; for(int i=front; i<=rear; i++) cout<<Q[i] << '\t'; }

void main() { clrscr(); int item, res ; char ch='y' ; while(ch=='y' || ch=='Y') { cout<<"\n\t enter element to be inserted : "; cin>> item; res = insert_in_Q(Q,item); // res= remove(Q) if( res==-1) { cout<<"n!!! sorry OVERFLOW !!! aborting## "; exit(1); } cout<<"\n \a\tnow the queue is : "; display (Q,front,rear); cout<<"\n\t\twant to insert more elements (y/n) :"; cin>>ch; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 51 Implementation of the Algorithm in Program: cout << "\n DO you want to remove items from the queue: "; cin >> ch; while(ch == 'y' || ch == 'Y') { int de = remove(Q); if (de == -1) cout << "\n Queue is empty, !!!!! UNDERFLOW !!!!!!"; else { cout << "\n Deleted item is : " << de; cout<<"\n \a\tnow the queue is : "; display (Q,front,rear); cout << "\n Do you want to remove more items from the queue: "; cin >> ch; } }}

LINKED LIST IMPLEMENTATION A queue can also be implemented with a linked list with both a head and a tail pointer. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 52 10 15 7 null 13 head_ptr tail_ptr

LINKED LIST IMPLEMENTATION Which end do you think is the front of the queue? Why? SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 53 10 15 7 null 13 head_ptr tail_ptr

LINKED LIST IMPLEMENTATION The head_ptr points to the front of the list. Because it is harder to remove items from the tail of the list. SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 54 10 15 7 null head_ptr 13 tail_ptr Front Rear

INSERTION IN THE QUEUE: Algorithm 1.Newptr = new Node 2.Newptr -> info = item; Newptr -> next = NULL 3.If Rear == NULL) then { 4.Front = Newptr 5.Rear = Newptr } 6.Else { 7.Rear -> next = Newptr 8.Rear = Newptr } 9.End SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 55

DELETION IN THE QUEUE: SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 56 Algorithm 1. If Front = NULL then 2. Print UNDERFLOW 3. Else { 4. Ptr = Front 5. If Front = Rear Then 6. Front = Rear = NULL 7. Else Front = Front - > next } 8. Delete ptr 9. End

#include struct node { int info; node *next; } *front,*newptr,*ptr,*save,*rear ; int itemdel; node* creat_new_node( int n) { ptr=new node; ptr->info=n; ptr->next=NULL; return ptr; } SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 57 Implementation of the Algorithm in Program: void insert_end (node* np) { if(front==NULL) front= rear=np; else { rear->next= np; rear=np; } } void display(node* np) { while (np != NULL) { cout info "; np = np->next ; } cout "; }

void delnode_q( ) { if (front==NULL) cout "; else { ptr = front; itemdel = ptr->info; front = front ->next; delete ptr; } void main() { front = rear = NULL; int inf ; char ch='y'; SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 58 Implementation of the Algorithm in Program: while(ch=='y' || ch=='Y') { clrscr(); cout<<"\n enter information of the new node.."; cin >> inf ; cout<<"\n creating new node ! ! press enter to continue..."; getch(); newptr = creat_new_node(inf); if( newptr == NULL) { cout<<"\n \n CANNOT CREATE NODE"; exit(1); getch(); } insert_end(newptr );

cout<<"\n now the queue is :"; display(front); cout<<"\n \a \t press y toenter new node, n to exit: " ; cin>>ch; } cout<<"\n Do you want to delete element (y/n): " ; cin >> ch; while (ch == 'y' || ch == 'Y') { delnode_q(); SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 59 Implementation of the Algorithm in Program: cout << "\n The deleted item is: " << itemdel; cout<<"\n now the Queue is: \n"; display(front); cout<<"\n Do you want to delete another element (y/n): " ; cin >> ch; } cout<<"\n now the Queue is: \n"; display(front); getch(); }

SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 60

SARAS M SRIVASTAVA, PGT (CS), KV, IISC, BANGALORE - 12 61 Questions

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