NCS 301 DATA STRUCTURE USING C

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1 NCS 301 DATA STRUCTURE USING C Unit-1 Part-4 Linked Lists Hammad Mashkoor Lari Assistant Professor Allenhouse Institute of Technology Introduction List refers to linear collection of data items. Example:-shopping list Data processing involves storing and processing data organized into lists. One such way of storing is using arrays. Advantages of arrays:- Easy to compute the address of an element in an array(physical relationship of data in memory). Disadvantages:- 1. Relatively expensive to insert and delete elements 2. Array usually occupies a block of memory space one cannot simply double or triple the size of array when required(arrays are called dense lists) Subject Notes by Hammad Lari 1

2 Continued. Another way of storing a list is to have each element in list contain a field called a link or pointer which contain the address of next element in the list. No adjacent space. Easy to delete and insert elements This is called linked lists Linked lists A linked list or one way list is a linear collection of data elements called nodes where linear order is given by means of pointers. Each node is divided into 2 parts:- 1. First part contains information about element 2. Second part called link or nextpointer field contains address of next node. Linked list with 3 nodes Pointer of last node contains a special value called null pointer which is invalid address(in practice 0 or negative number is used for null) List also contains list pointer variable called or name which contains address of first node in list. x Subject Notes by Hammad Lari 2

3 Representation of Linked Lists in memory Let LIST be a linked list. LIST requires two linear arrays (INFO & LINK). List also requires a variable name such as START and nextpointer sentinel NULL. We choose null=0. Example:- Refer page 5.4 from Data structures by Seymour Lipschutz(schaum) Declaration for linear linked list in memory Struct node { Int a ; Struct node *next; }; Typedef struct node NODE; NODE *; Types of linked list 1. Singly linked list-linear(we cannot access the predecessor of node from current node) 2. Doubly ll-multiple links, accessing both predecessor and successor 3. Circular ll-no beginning and no end(sorting the address of very first node in link field of last node) 4. Circular doubly ll-successor and predecessor pointer in circular manner. Operations on Linked list 1. Creation 2. Insertion 3. Searching 4. Deletion 5. Traversing 6. Searching 7. Display Subject Notes by Hammad Lari 3

4 Singly Linked list In C a ll is created using structure,pointers and dyanamic memory allocation. Struct node { Int num; Struct node *ptr; //pointer to node }; Typedef struct node NODE //type def making it adt NODE *; //pointer to node of ll Start=(NODE*)malloc (sizeof(node));//dynamic memory allocation //when this line is executed NODE is allocated and assigns HEAD as ing address of NODE(head is the external pointer) NODE num ptr Singly Linked list NODE num ptr Now we can assign values Start->number=30; Start->ptr= \0 //null pointer Start->ptr=(NODE *) malloc(sizeof(node)); Start->ptr.num=100; Start->ptr.ptr= \0 Subject Notes by Hammad Lari 4

5 Inserting nodes in Singly linked list To insert an element following things should be done 1. Allocating a node 2. Assigning the data 3. Adjusting the pointers Three instances of inserting 1. At the beginning 2. At the end 3. At specified position Insertion at the beginning Node A Before Insertion Node A After Insertion 100 ptr New Node Subject Notes by Hammad Lari 5

6 Algorithm-insertion at beginning Insert(,item) 1. Initialize NODE *p 2. p=(node *)malloc(sizeof(node)) 3. if(p==null) print insertion was not possible and exit for program 4. else 1. If(==null) P->next=null; 2. Else P->next=; 3. Start=p; Insertion at the end Before Insertion After Insertion ptr 100 x Subject Notes by Hammad Lari 6

7 Algorithm-insertion at the end Insert(,item) 1. Initialize node *p,item 2. P=(NODE *)malloc(sizeof(node)) 3. If(p==NULL) Print NODE was not created and exit for program. 4. else 1. P->info=item 2. P->next= \0 3. If(==NULL) Start=p 4. Else Temp= Repeat until (temp->next== \0 ) Temp=temp->next Temp->next=p Insertion at the middle or specific location Node A Node B Before Insertion Node A Node B After Insertion Subject Notes by Hammad Lari 7

8 Algorithm-insertion at specific position 1. Initialize NODE *p,temp,loc 2. p=(node *)malloc(sizeof(node)) 3. If(p==NULL) 4. Else Print NODE is not created and exit from program. 1. p->info=item 2. if(==null) 1. =p 2. P->next=null 3. Else(initialize counter I and temp pointers) 1.temp= 2.i=1 3.Repeat until i<loc 1.temp=temp->next 2.i++ 4.p=temp->next 5.temp->next=p Deleting first node ptr Before deletion After deletion Subject Notes by Hammad Lari 8

9 Algorithm-Delete from beginning delete() 1. Check for underflow? 1. If =null then 2. print no nodes 3. Exit 2. Set ptr= 3. Set =->next 4. Print element deleted ptr->info 5. Free(ptr) Deleting last node loc ptr x Before deletion x After deletion Subject Notes by Hammad Lari 9

10 Algorithm-deletion from end delete() 1. Check for underflow? 1. If =null then 2. print no nodes 3. Exit 2. If ->next=null then 1. Set ptr= 2. Set =null 3. Print element deleted is ptr->info 4. Free(ptr) 3. Set ptr= 4. Repeat until ptr->next!=null 1. Set loc=ptr 2. Set ptr=ptr->next 5. Set loc->next=null 6. Free(ptr) Deleting node from specific position x Before deletion x After deletion Subject Notes by Hammad Lari 10

11 Algorithm-deletion from specific position delete() 1. Check for underflow? 1. If =null then 2. print no nodes 3. Exit 2. Initialize counter, I and pointers 1. Node *temp, node *ptr; 2. Set i=0 3. Set ptr= 3. Repeat steps 4 to 9 until i<=loc 4. Set temp=ptr 5. Set ptr=ptr->next 6. Set i=i+1 7. Print element deleted is 8. Set temp->next=ptr->new 9. Free(ptr) Circular Linked lists A circular linked list is a type of singly linked list in which the link field of the last node contains the address of first node of the list. List contains list pointer variable called and last which contains address of first node and last node in list. Linked list with 3 nodes x last Subject Notes by Hammad Lari 11

12 Algorithm-insertion at beginning 1. Initialize NODE *P 2. p=(node *)malloc(sizeof(node)) 3. If(p==NULL) 1. Print insertion was not possible 4. Else 1. p->info=item 2. if(==null) 1. Start=last=p 2. P->next= 3. Else 1. p->next= 2. =p 3. last->next=p Algorithm-insertion at end 1. Initialize NODE *p 2. p=(node*)malloc(sizeof(node)) 3. If(p==NULL) 1. Print insertion was not possible. 4. Else 1. P->info=item 2. If(==NULL) 1.=last=p 2.p->next= 3. Else 1.Last->next=p 2.Last=p 3.Last->next= Subject Notes by Hammad Lari 12

13 Algorithm-deletion from beginning 1. Initialize NODE *p 2. if(==null) 1. print 'UNDERFLOW'. 3. else 1. p= 2. =->next 3. last->next= 4. print p->info 5. free(p) Algorithm-deletion from end 1. Initialize NODE *p,*temp. 2. if(==null) 1. print 'UNDERFLOW' 3. else 1. p= 2. repeat untill p->next!= 1. temp=p 2. p=p->next 3. temp->next= 4. last=temp 5. print p->info 6. free(p) Subject Notes by Hammad Lari 13

14 Doubly Linked lists Disadvantage of Singly linked list:- 1. Inability to traverse the list in the backward direction. A doubly linked list provides bi directional traversing. Each node in D.L has two fields. prev data next last Doubly Linked list with 3 nodes x x List contains list pointer variable called and last which contains address of first node and last node in list. Structure Doubly linked list struct node { struct node *prev; struct node *next; char info; } typedef struct node NODE NODE *; NODE *last; Subject Notes by Hammad Lari 14

15 Algorithm-insertion at beginning 1. Initialize NODE *p 2. p=(node *)malloc(sizeof(node)) 3. p->info=item 4. p->prev=null 5. if(==null) 1. =last=p 2. p->next=null 6. else 1. p->next= 2. ->prev=p 3. =p Algorithm-insertion at end 1. Initialize NODE *p. 2. p=(node *)malloc(sizeof(node)) 3. p->info= item 4. p->next=null 5. if(==null) 1. =last=p 2. p->prev=null 6. else 1. last->next=p 2. p->prev=last 3. last=p Subject Notes by Hammad Lari 15

16 Algorithm-deletion from beginning 1. Initialize *p. 2. if(==null) 1. print ''UNDERFLOW'' 3. else 1. p= 2. =->next 3. ->prev=null 4. print p->info 5. free(p) Algorithm-deletion from end 1. Initialize *p. 2. if(==null) 1. print "UNDERFLOW" 3. else 1. If(last->prev==null) 1. P=last 2. Last->last->prev 3. Last->next=null 2. print p->info 3. free(p) Subject Notes by Hammad Lari 16

17 Class Website Subject Notes by Hammad Lari 17