Overview
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.
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Link − Each Link of a linked list can store a data called an element.
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Next − Each Link of a linked list contain a link to next link called Next.
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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.
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LinkedList contains an link element called first.
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Each Link carries a data field(s) and a Link Field called next.
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Each Link is linked with its next link using its next link.
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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.
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Simple Linked List − Item Navigation is forward only.
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Doubly Linked List − Items can be navigated forward and backward way.
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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.
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Insertion − add an element at the beginning of the list.
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Deletion − delete an element at the beginning of the list.
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Display − displaying complete list.
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Search − search an element using given key.
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Delete − delete an element using given key.
Insertion Operation
Insertion is a three step process −
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Create a new Link with provided data.
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Point New Link to old First Link.
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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 −
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Get the Link pointed by First Link as Temp Link.
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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. −
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Get the Link pointed by First Link as Current Link.
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Check if Current Link is not null and display it.
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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.
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Sort − sorting a list based on a particular order.
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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;
}
Example
LinkedListDemo.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
struct node {
int data;
int key;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
//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(" ]");
}
//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;
}
//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;
}
//is list empty
bool isEmpty(){
return head == NULL;
}
int length(){
int length = 0;
struct node *current;
for(current = head; current!=NULL;
current = current->next){
length++;
}
return length;
}
//find a link with given key
struct node* find(int key){
//start from the first link
struct node* current = head;
//if list is empty
if(head == NULL){
return NULL;
}
//navigate through list
while(current->key != key){
//if it is last node
if(current->next == NULL){
return NULL;
} else {
//go to next link
current = current->next;
}
}
//if data found, return the current Link
return current;
}
//delete a link with given key
struct node* delete(int key){
//start from the first link
struct node* current = head;
struct node* previous = NULL;
//if list is empty
if(head == NULL){
return NULL;
}
//navigate through list
while(current->key != key){
//if it is last node
if(current->next == NULL){
return NULL;
} else {
//store reference to current link
previous = current;
//move to next link
current = current->next;
}
}
//found a match, update the link
if(current == head) {
//change first to point to next link
head = head->next;
} else {
//bypass the current link
previous->next = current->next;
}
return current;
}
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;
}
}
}
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;
}
main() {
insertFirst(1,10);
insertFirst(2,20);
insertFirst(3,30);
insertFirst(4,1);
insertFirst(5,40);
insertFirst(6,56);
printf("Original List: ");
//print list
printList();
while(!isEmpty()){
struct node *temp = deleteFirst();
printf("nDeleted value:");
printf("(%d,%d) ",temp->key,temp->data);
}
printf("nList after deleting all items: ");
printList();
insertFirst(1,10);
insertFirst(2,20);
insertFirst(3,30);
insertFirst(4,1);
insertFirst(5,40);
insertFirst(6,56);
printf("nRestored List: ");
printList();
printf("n");
struct node *foundLink = find(4);
if(foundLink != NULL){
printf("Element found: ");
printf("(%d,%d) ",foundLink->key,foundLink->data);
printf("n");
} else {
printf("Element not found.");
}
delete(4);
printf("List after deleting an item: ");
printList();
printf("n");
foundLink = find(4);
if(foundLink != NULL){
printf("Element found: ");
printf("(%d,%d) ",foundLink->key,foundLink->data);
printf("n");
} else {
printf("Element not found.");
}
printf("n");
sort();
printf("List after sorting the data: ");
printList();
reverse(&head);
printf("nList after reversing the data: ");
printList();
}
Output
If we compile and run the above program then it would produce following Output −
Original List: [ (6,56) (5,40) (4,1) (3,30) (2,20) (1,10) ] Deleted value:(6,56) Deleted value:(5,40) Deleted value:(4,1) Deleted value:(3,30) Deleted value:(2,20) Deleted value:(1,10) List after deleting all items: [ ] Restored List: [ (6,56) (5,40) (4,1) (3,30) (2,20) (1,10) ] Element found: (4,1) List after deleting an item: [ (6,56) (5,40) (3,30) (2,20) (1,10) ] Element not found. List after sorting the data: [ (1,10) (2,20) (3,30) (5,40) (6,56) ] List after reversing the data: [ (6,56) (5,40) (3,30) (2,20) (1,10) ]