Module III. Linear Data Structures and their Linked Storage Representation

Transcription

1 Module III Linear Data Structures and their Linked Storage Representation 3.1 Linked List Linked list is the collection of inter connected nodes with a head node representing the first node and a tail node representing the last node of it. A node can be viewed as a block consisting of two major fields: a data field and a pointer field. The pointer field is used to interconnect nodes of a list. Below diagram depicts the linked list setup. Tail 3.2 Linked list types There are few variants of linked lists. Below diagram shows a brief classification of Linked Lists. Linked List NULL Singly LL Circular LL Doubly LL Singly Circular LL Doubly Circular LL Regarding these variants of LL, explanations and examples are given in subsequent sections of the notes. 3.2 Linked List Representation A simple representation of singly linked list would look like the below: struct node int data; struct node *next; ;

2 struct node *newnode; With the above declaration we can create a node of the pattern below: data *next newnode Initially, the pointer field of the first node in singly linked list would contain NULL value. Instruction that makes it is: newnode->next = NULL; Note: Structure variables fields of self referential type are accessed through -> (arrow operator) Now, let us try to understand few conventions w.r.t linked lists. Consider below given list h h h 40 NULL head (1000h) (1008h) (1016h) tail (1024h) In this list, head node contains data = 10 and tail node contains data = 40. This list has 4 nodes that are interconnected. Head node is connected to the next node since the pointer value contains the address of next node. Tail node is not linked to any node since its pointer value is NULL. struct node *head, *tail, *newnode; // variables declared of type struct node head = (struct node *) malloc (1 * sizeof(struct node)); This instruction creates one node of type struct. Memory gets allocated using DMA function malloc(). Created node in the above instruction is referred to as head. It can be any other name as well. head->data = 10; // assigns head node s data field with 10 head->next = NULL; //assigning pointer value to NULL 10 NULL head; tail tail = head; // assigning the reference of head to tail. This means both head and tail are referring to the same node. Now, let us add a new node to this list. newnode = (struct node *) malloc (1 * sizeof(struct node)); newnode->data = 20; newnode->next = NULL; 10 NULL 10 NULL Mr. Head; Nischaykumar tail Hegde, newnode CSE, VCET, Puttur

3 The above nodes can be connected using the following instructions: head->next = newnode; // assigning head node s pointer value with address of newnode h 20 NULL head; tail (1000h) newnode (1008h) Now, if we execute the instruction, tail = newnode; tail & newnode both refer to the node with value 20. In this way, linked lists can be created. 3.3 Operations on Linked Lists Major operations performed on linked lists are inserting a node, deleting a node, searching a node and traversing the list to display all of its nodes. a) Inserting a node: Node can be inserted at the beginning, at the end or anywhere in the linked list h h h 40 NULL head (1000h) (1008h) (1016h) tail (1024h) Consider the above list. Suppose we wish to insert a node at the beginning, following set of instruction are to be executed. newnode = (struct node *) malloc (1 * sizeof(struct node)); newnode->data = 50; newnode->next = head; h head = newnode; h h h 40 NULL (1000h) (1008h) (1016h) tail (1024h) h head; newnode Suppose we wish to insert a node at the end, following set of instruction are to be executed h h h h head (1000h) (1008h) (1016h) tail (1024h) newnode = (struct node *) malloc (1 * sizeof(struct node)); 80 NULL newnode->data = 80; newnode->next = NULL; 80 NULL (1032h)

4 Take a temporary variable of type struct node, traverse the list until you reach the last node (i.e tail ) while(temp->next!=null) temp=temp->next; temp->next = newnode; tail = newnode; Now let us see how to insert a node at a particular position in the list. For this, we need to ask user to specify after which node in the list he would want to insert. Call it as key node. This can be realized as below: temp h h h h head (1000h) (1008h) (1016h) tail (1024h) Key = h Newnode (1040h) 80 NULL (1032h) Take a temporary variable of type struct node, traverse the list until you reach the desired node (i.e 30) while(temp->data!=key) temp=temp->next; 100 NULL newnode (1040h) newnode->next = temp->next; temp->next = newnode; b) Deleting a node: A node in the list can be deleted using the standard function free ( ). Let us see an example to understand delete operations on linked list h h 30 NULL 40 NULL head (1000h) temp2 (1008h) temp(1016h) tail (1024h) Let us try to delete node with 30 data value. Take two temporary variables and position them to key node and the previous node of it.

5 Now, key =30. While(temp->data!=key) temp=temp->next; While(temp2->next!=key) temp2=temp2->next; temp2->next = temp->next; temp->next = NULL; free(temp); Below C program creates a singly linked list and performs few operations like insert, delete, display, search, insert and delete at specific positions in the list. #include <stdio.h> #include <stdlib.h> struct node int data; struct node *next; ; struct node *head, *tail,*temp, *temp2; void create(); void delet(); void dele_spec(); void display(); void spec_ins(); int search(int); int num,con=1,ch,key,f; void main()

6 clrscr(); head=null; printf("1.create\n2.delete\n3.delete Specific\n4.Insert After Specific node\n5.display\n6. Search\n7.Exit\n"); while(1) printf("enter choice\n"); scanf("%d",&ch); switch(ch) case 1: printf("enter number\n"); scanf("%d",&num); create(); case 2: delet(); case 3: dele_spec(); case 4: spec_ins(); case 5: display(); case 6: printf("enter the node data to be searched\n"); scanf("%d",&key); f=search(key); if(f==1) printf("node FOUND\n"); printf("node NOT FOUND\n"); case 7: exit(0);

7 void create() if(head==null) head = (struct node*)malloc(1*sizeof(struct node)); head->data=num; head->next=null; tail=head; temp= (struct node*)malloc(1*sizeof(struct node)); temp->data=num; tail->next=temp; temp->next=null; tail=temp; void delet() if(head==null) printf("list is empty\n"); temp=head; temp = temp->next; free(head); head=temp;

8 void dele_spec() int key; printf("enter the node to be deleted\n"); scanf("%d",&key); temp=head; temp2=head; while(temp->data!=key) temp=temp->next; while(temp2->next!=temp) temp2=temp2->next; if(temp->next==null) temp2->next=null; free(temp); tail=temp2; temp2->next=temp->next; free(temp); void spec_ins()

9 int key; printf("enter the node info next to which to be inserted\n"); scanf("%d",&key); printf("enter data for newnode\n"); scanf("%d",&num); temp2= (struct node*)malloc(1*sizeof(struct node)); temp2->data=num; temp=head; while(temp->data!=key) temp=temp->next; temp2->next=temp->next; temp->next=temp2; void display() if(head==null) printf("list empty\n"); temp=head; while(temp!=null) printf("%d\t",temp->data); temp=temp->next;

10 int search(int key) int flag=0; temp=head; while(temp!=null) if(temp->data==key) flag=1; return flag; temp=temp->next; return flag; Advantages of Linked Lists They are a dynamic in nature which allocates the memory when required. Insertion and deletion operations can be easily implemented. Stacks and queues can be easily executed. Linked List reduces the access time. Disadvantages of Linked Lists The memory is wasted as pointers require extra memory for storage. No element can be accessed randomly; it has to access each node sequentially. Reverse Traversing is difficult in linked list. Applications of Linked Lists Linked lists are used to implement stacks, queues, graphs, etc. Linked lists let you insert elements at the beginning and end of the list. In Linked Lists we don t need to know the size in advance. 3.4 Types of Linked Lists

11 Singly Linked List : Singly linked lists contain nodes which have a data part as well as an address part i.e. next, which points to the next node in sequence of nodes. The operations we can perform on singly linked lists are insertion, deletion and traversal. Doubly Linked List : In a doubly linked list, each node contains two links the first link points to the previous node and the next link points to the next node in the sequence. Circular Linked List : Singly Circular LL: In the circular linked list the last node of the list contains the address of the first node and forms a circular chain. Doubly Circular LL: In the doubly circular linked list the last node s next ptr field will have the address of start (head) node and the start (head) node s previous ptr field will have the address of last (tail) node. Below diagram shows its pictorial representation.

12 3.5 Header Linked List Head 3 Header Header linked list is similar to Singly linked List but the difference is that in this type of list, there exists a special node called header, which either contains information regarding total nodes in the list or the address of the last node in the whole list. C Program to implement header linked list is shown below (For execution purpose) #include <stdio.h> #include <conio.h> #include <stdlib.h> struct node int data; struct node *next; ; struct node *head, *header,*last,*temp, *newnode; void create(); void delet(); void display(); int num,count=0,ch; void main() clrscr(); head=null;

13 printf("1.create\n2.delete\n3.display\n4.exit\n"); while(1) printf("enter choice\n"); scanf("%d",&ch); switch(ch) case 1: if(head==null) header = (struct node*)malloc(1*sizeof(struct node)); header->data=count; printf("enter number\n"); scanf("%d",&num); create(); case 2: delet(); case 3: display(); case 4: exit(0); void create() if (head == NULL) head = (struct node*)malloc(1*sizeof(struct node)); head->data=num; head->next = NULL; header->next = head;

14 tail =head; count++; header->next = count; newnode = (struct node*)malloc(1*sizeof(struct node)); newnode->data=num; newnode->next=null; tail->next=newnode; tail=newnode; count++; header->data=count; void delet() if(head->data==0) printf("list is empty\n"); temp=head; while(temp->next!=last) temp=temp->next; free(tail); tail =temp; tail->next=null; count--;

15 header->data=count; void display() if(head==null) printf("list empty\n"); temp=head; while(temp!=null) printf("%d\t",temp->data); temp=temp->ptr; printf("\nheader Information:%d nodes\n",header->data); C Program to implement header linked list is shown below (For Exam purpose) #include <stdio.h> #include <stdlib.h> struct node int data; struct node *next; ; struct node *head,*header,*tail,*temp,*newnode; void create(int); void delet(); void display(); int num,count=0,ch;

16 void main() clrscr(); header=(struct node *)malloc(1*sizeof(struct node)); header->data=count; header->next=null; create(10); create(20); create(30); delet(); display(); void create(int num) if(head==null) head=(struct node*)malloc(1*sizeof(struct node)); head->data=num; head->next=null; tail=head; count++; newnode = (struct node*)malloc(1*sizeof(struct node)); newnode->data=num; newnode->next=null; tail->next=newnode; tail=newnode; count++; header->data=count;

17 void delet() if(header==null) printf("list is empty\n"); temp=head; while(temp->next!=tail) temp=temp->next; free(tail); tail =temp; tail->next=null; count--; header->data=count; void display() if(head==null) printf("list empty\n");

18 temp=head; while(temp!=null) printf("%d\t",temp->data); temp=temp->next; printf("\nheader Information:%d\n",header->data); 3.5 Linked implementation of Stack #include <stdio.h> #include <stdlib.h> struct Node int Data; struct Node *next; *top; void popstack() struct Node *temp, *var=top; if(var==top) top = top->next; free(var); printf("\nstack Empty"); void push(int value) struct Node *temp;

19 temp=(struct Node *)malloc(sizeof(struct Node)); temp->data=value; if (top == NULL) top=temp; top->next=null; temp->next=top; top=temp; void display() struct Node *var=top; if(var!=null) printf("\nelements are as:\n"); while(var!=null) printf("\t%d\n",var->data); var=var->next; printf("\n"); printf("\nstack is Empty"); int main(int argc, char *argv[])

20 int i=0; top=null; printf(" \n1. Push to stack"); printf(" \n2. Pop from Stack"); printf(" \n3. Display data of Stack"); printf(" \n4. Exit\n"); while(1) printf(" \nchoose Option: "); scanf("%d",&i); switch(i) case 1: int value; printf("\nenter a valueber to push into Stack: "); scanf("%d",&value); push(value); display(); case 2: popstack(); display(); case 3: display();

21 case 4: struct Node *temp; while(top!=null) temp = top->next; free(top); top=temp; exit(0); default: printf("\nwrong choice for operation"); 3.6 Merging of two lists #include<stdio.h> #include<stdlib.h> struct node int data; struct node *next; ; void insert_list1(); void insert_list2(); void display(); void merge_list();

22 struct node *list1, *list2,*list3,*temp1,*temp2,*temp3,*temp4; void main() int ch; clrscr(); printf("1 for insert in first linklist\n"); printf("2 for insert in second linklist\n"); printf("3 for display first & second linklist\n"); printf("4 for merge linklist\n"); printf("5 for exit\n"); while(1) printf("\nenter ur choice:"); scanf("%d",&ch); switch(ch) case 1: insert_list1(); case 2: insert_list2(); case 3: display(); case 4: merge_list(); case 5: exit(0); void merge_list() temp1=list1;

23 temp2=list2; while(temp1!=null temp2!=null) temp3=(struct node*)malloc(1*sizeof(struct node)); if(list3==null) list3=temp3; temp4=temp3; if(temp1->data<temp2->data) temp3->data=temp1->data; temp4->next=temp3; temp4=temp3; temp1=temp1->next; temp3->data=temp2->data; temp4->next=temp3; temp4=temp3; temp2=temp2->next; if(temp2==null) while(temp1!=null) temp3=(struct node*)malloc(1*sizeof(struct node)); temp3->data=temp1->data; temp4->next=temp3; temp4=temp3;

24 temp1=temp1->next; if(temp1==null) while(temp2!=null) temp3=(struct node*)malloc(1*sizeof(struct node)); temp3->data=temp2->data; temp4->next=temp3; temp4=temp3; temp2=temp2->next; temp3->next=null; void insert_list1() struct node *new; if(list1==null) list1=(struct node *)malloc(sizeof(struct node)); printf("enter the info"); scanf("%d",&list1->data); list1->next=null; temp1=list1;

25 new=(struct node *)malloc(sizeof(struct node)); printf("enter the info"); scanf("%d",&new->data); new->next=null; temp1->next=new; temp1=temp1->next; void insert_list2() struct node *new; if(list2==null) list2=(struct node *)malloc(sizeof(struct node)); printf("enter the info"); scanf("%d",&list2->data); list2->next=null; temp2=list2; new=(struct node *)malloc(sizeof(struct node)); printf("enter the info"); scanf("%d",&new->data); new->next=null; temp2->next=new; temp2=temp2->next;

26 void display() temp1=list1; temp2=list2; printf("\nthe Information of First linklist:"); while(temp1!=null) printf("%d ",temp1->data); temp1=temp1->next; printf("\nthe Information of Second linklist:"); while(temp2!=null) printf("%d ",temp2->data); temp2=temp2->next; temp3=list3; printf("\nmerged List:"); while(temp3!=null) printf("%d ",temp3->data); temp3=temp3->next;