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DSA using C - Linked List
  • 时间：2024-09-08

DSA using C - Linked List

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Overview

Linked List is a sequence of pnks which contains items. Each pnk contains a connection to another pnk. Linked pst the second most used data structure after array. Following are important terms to understand the concepts of Linked List.

    Link − Each Link of a pnked pst can store a data called an element.

    Next − Each Link of a pnked pst contain a pnk to next pnk called Next.

    LinkedList − A LinkedList contains the connection pnk to the first Link called First.

Linked List Representation

Linked List

As per above shown illustration, following are the important points to be considered.

    LinkedList contains an pnk element called first.

    Each Link carries a data field(s) and a Link Field called next.

    Each Link is pnked with its next pnk using its next pnk.

    Last Link carries a Link as null to mark the end of the pst.

Types of Linked List

Following are the various flavours of pnked pst.

    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 pnk of the first element as next and and first element has pnk to last element as prev.

Basic Operations

Following are the basic operations supported by a pst.

    Insertion − add an element at the beginning of the pst.

    Deletion − delete an element at the beginning of the pst.

    Display − displaying complete pst.

    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.

Linked List Insert First 


//insert pnk at the first location
void insertFirst(int key, int data){
   //create a pnk
   struct node *pnk = (struct node*) malloc(sizeof(struct node));
   pnk->key = key;
   pnk->data = data;
   
   //point it to old first node
   pnk->next = head;
   
   //point first to new first node
   head = pnk;
}

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.

Linked List Delete First 


//delete first item
struct node* deleteFirst(){
   //save reference to first pnk
   struct node *tempLink = head;
   
   //mark next to first pnk as first 
   head = head->next;
   
   //return the deleted pnk
   return tempLink;
}

Navigation Operation

Navigation is a recursive step process and is basis of many operations pke 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.

Linked List Navigation

Note −


//display the pst
void printList(){
   struct node *ptr = head;
   printf("
[ ");
   
   //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 pst.

    Sort − sorting a pst based on a particular order.

    Reverse − reversing a pnked pst.

Sort Operation

We ve used bubble sort to sort a pst.


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 pnked pst.


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 <stdpb.h>
#include <stdbool.h>

struct node {
   int data;
   int key;
   struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;

//display the pst
void printList(){
   struct node *ptr = head;
   printf("
[ ");
   
   //start from the beginning
   while(ptr != NULL){        
      printf("(%d,%d) ",ptr->key,ptr->data);
      ptr = ptr->next;
   }
   printf(" ]");
}
//insert pnk at the first location
void insertFirst(int key, int data){
   //create a pnk
   struct node *pnk = (struct node*) malloc(sizeof(struct node));
   pnk->key = key;
   pnk->data = data;
   
   //point it to old first node
   pnk->next = head;
   
   //point first to new first node
   head = pnk;
}
//delete first item
struct node* deleteFirst(){
   //save reference to first pnk
   struct node *tempLink = head;
   
   //mark next to first pnk as first 
   head = head->next;
   
   //return the deleted pnk
   return tempLink;
}
//is pst 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 pnk with given key
struct node* find(int key){
   //start from the first pnk
   struct node* current = head;

   //if pst is empty
   if(head == NULL){
      return NULL;
   }
   //navigate through pst
   while(current->key != key){
      //if it is last node
      if(current->next == NULL){
         return NULL;
      } else {
         //go to next pnk
         current = current->next;
      }
   }
   //if data found, return the current Link
   return current;
}
//delete a pnk with given key
struct node* delete(int key){
   //start from the first pnk
   struct node* current = head;
   struct node* previous = NULL;
   
   //if pst is empty
   if(head == NULL){
      return NULL;
   }
   //navigate through pst
   while(current->key != key){
      //if it is last node
      if(current->next == NULL){
         return NULL;
      } else {
         //store reference to current pnk
         previous = current;
         
         //move to next pnk
         current = current->next;             
      }
   }
   //found a match, update the pnk
   if(current == head) {
      //change first to point to next pnk
      head = head->next;
   } else {
      //bypass the current pnk
      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 pst
   printList();

   while(!isEmpty()){            
      struct node *temp = deleteFirst();
      printf("
Deleted value:");  
      printf("(%d,%d) ",temp->key,temp->data);        
   }         
   printf("
List after deleting all items: ");          
   printList();
   insertFirst(1,10);
   insertFirst(2,20);
   insertFirst(3,30);
   insertFirst(4,1);
   insertFirst(5,40);
   insertFirst(6,56); 
   printf("
Restored List: ");  
   printList();
   printf("
");  

   struct node *foundLink = find(4);
   if(foundLink != NULL){
      printf("Element found: ");  
      printf("(%d,%d) ",foundLink->key,foundLink->data);  
      printf("
");  
   } else {
      printf("Element not found.");  
   }
   delete(4);
   printf("List after deleting an item: ");  
   printList();
   printf("
");
   foundLink = find(4);
   if(foundLink != NULL){
      printf("Element found: ");  
      printf("(%d,%d) ",foundLink->key,foundLink->data);  
      printf("
");  
   } else {
      printf("Element not found.");  
   }
   printf("
");  
   sort();
   printf("List after sorting the data: ");  
   printList();
   reverse(&head);
   printf("
List 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) ]
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