Data Structure - Linked List
Linked List Basics:
A linked-list is a sequence of data structures which are connected together via links.
Linked List is a sequence of links which contains items. Each link contains a connection to another link. Linked list the second most used data structure after array. Following are important terms to understand the concepts of Linked List.
- Link − Each Link of a linked list can store a data called an element.
- Next − Each Link of a linked list contain a link to next link called Next.
- LinkedList − A LinkedList contains the connection link to the first Link called First.
Linked List Representation
As per above shown illustration, following are the important points to be considered.
- LinkedList contains an link element called first.
- Each Link carries a data field(s) and a Link Field called next.
- Each Link is linked with its next link using its next link.
- Last Link carries a Link as null to mark the end of the list.
Types of Linked List:
Following are the various flavours of linked list.
- Simple Linked List − Item Navigation is forward only.
- Doubly Linked List − Items can be navigated forward and backward way.
- Circular Linked List − Last item contains link of the first element as next and and first element has link to last element as prev.
Basic Operations:
Following are the basic operations supported by a list.
- Insertion − add an element at the beginning of the list.
- Deletion − delete an element at the beginning of the list.
- Display − displaying complete list.
- Search − search an element using given key.
- Delete − delete an element using given key.
Insertion Operation
Insertion is a three step process −
- Create a new Link with provided data.
- Point New Link to old First Link.
- Point First Link to this New Link.
//insert link at the first location
void insertFirst(int key, int data){
//create a link
struct node *link = (struct node*) malloc(sizeof(struct node));
link->key = key;
link->data = data;
//point it to old first node
link->next = head;
//point first to new first node
head = link;
}
Deletion Operation
Deletion is a two step process −
- Get the Link pointed by First Link as Temp Link.
- Point First Link to Temp Link's Next Link.
//delete first item
struct node* deleteFirst(){
//save reference to first link
struct node *tempLink = head;
//mark next to first link as first
head = head->next;
//return the deleted link
return tempLink;
}
Navigation Operation:
Navigation is a recursive step process and is basis of many operations like search, delete etc. −
- Get the Link pointed by First Link as Current Link.
- Check if Current Link is not null and display it.
- Point Current Link to Next Link of Current Link and move to above step.
Note −
//display the list
void printList(){
struct node *ptr = head;
printf("\n[ ");
//start from the beginning
while(ptr != NULL){
printf("(%d,%d) ",ptr->key,ptr->data);
ptr = ptr->next;
}
printf(" ]");
}
Advanced Operations
Following are the advanced operations specified for a list.
- Sort − sorting a list based on a particular order.
- Reverse − reversing a linked list.
Sort Operation
We've used bubble sort to sort a list.
void sort(){
int i, j, k, tempKey, tempData ;
struct node *current;
struct node *next;
int size = length();
k = size ;
for ( i = 0 ; i < size - 1 ; i++, k-- ) {
current = head ;
next = head->next ;
for ( j = 1 ; j < k ; j++ ) {
if ( current->data > next->data ) {
tempData = current->data ;
current->data = next->data;
next->data = tempData ;
tempKey = current->key;
current->key = next->key;
next->key = tempKey;
}
current = current->next;
next = next->next;
}
}
}
Reverse Operation
Following code demonstrate reversing a single linked list.
void reverse(struct node** head_ref) {
struct node* prev = NULL;
struct node* current = *head_ref;
struct node* next;
while (current != NULL) {
next = current->next;
current->next = prev;
prev = current;
current = next;
}
*head_ref = prev;
}
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