DoublyLinkedList

Author: Monik09

doubleLinkedList/doubleLinkedList.c

@@ -12,28 +12,27 @@ struct node *head = NULL, *last = NULL;
 
 struct node *createNode(int key)
 {
-	head = (struct node *)malloc(sizeof(struct node));
+	head = (struct node *)malloc(sizeof(struct node)); //allocate the required space to *node variable
 	head->data = key;
 	head->next = NULL;
 	head->prev = NULL;
 	last = head;
 	return head;
 }
 
-struct node *additionOfNodeAtBeginning( int key)
+struct node *additionOfNodeAtBeginning(int key) //adding at the beginning of the linked list
 {
 	struct node *temp;
 	temp = (struct node *)malloc(sizeof(struct node));
 	temp->data = key;
-	temp->next = NULL;
-	temp->next = head;
-	temp->prev = NULL;
+	temp->next = head; //making temp variable point to head of the linked list
+	temp->prev = NULL; //pointing the prev of temp to NULL pointer
 	head->prev = temp;
 	head = temp;
 	return head;
 }
 
-struct node *additionOfNodeAtEnding( int key)
+struct node *additionOfNodeAtEnding(int key) //adding the element at the last of the linked list
 {
 	struct node *temp;
 	temp = (struct node *)malloc(sizeof(struct node));
@@ -46,15 +45,20 @@ struct node *additionOfNodeAtEnding( int key)
 	return last;
 }
 
-struct node *additionOfNodeAtRandomeIndex( int key, int index)
+struct node *additionOfNodeAtRandomeIndex(int key, int index) //adding the element at the given index
 {
 	struct node *temp;
 	temp = (struct node *)malloc(sizeof(struct node));
 	temp->data = key;
 	temp->next = NULL;
-	struct node *temp1, *temp2, previous;
+	if (index == 0)
+	{
+		return additionOfNodeAtBeginning(key);
+	}
+	struct node *temp1, *temp2;
 	temp1 = head;
 	int i = 0;
+	//iterating through the list till the iterator variable is index or list is empty
 	while (i < index - 1 && temp1->next != NULL)
 	{
 		temp1 = temp1->next;
@@ -72,52 +76,62 @@ struct node *additionOfNodeAtRandomeIndex( int key, int index)
 	return head;
 }
 
-struct node *deletingFromBeginning()
+struct node *deletingFromBeginning() //deleting the element at head
 {
 	struct node *temp;
 	temp = head;
-	head = head->next;
+	head = head->next; //making the head pointer to point the element next to it
 	head->prev = NULL;
-	free(temp);
+	free(temp); //free the space occupied by former head pointer
 	return head;
 }
 
-struct node *deletingFromEnding()
+struct node *deletingFromEnding() //deleting the element from the ending
 {
 	struct node *temp, *temp2;
-	temp=last->prev;
-	temp2=last;
-	temp->next=NULL;
-	last=temp;
+	temp = last->prev; //temp pointer pointing to the second last element of linked list
+	temp2 = last;	   //temp2 pointing to last element
+	temp->next = NULL;
+	last = temp; //make second last pointer as last element
 	free(temp2);
 	return head;
 }
 
-struct node *deletingFromRandomIndex(int index)
+struct node *deletingFromRandomIndex(int index) //deleting the element from given index
 {
 	struct node *temp, *temp2;
 	temp = head;
 	int i = 0;
-	while (i < index - 1)
+	while (temp != NULL && i < index)
 	{
 		i++;
 		temp = temp->next;
 	}
-	if (temp->next == NULL)
+	if (index == 0)
+	{
+		return deletingFromBeginning();
+	}
+	else if (temp == last)
 	{
 		return deletingFromEnding();
 	}
-	temp2 = temp->next;
-	temp2->next->prev = temp;
-	temp->next = temp->next->next;
-	free(temp2);
+	else if (temp != NULL) //if temp is NULL the index is out of Bound
+	{
+		temp->prev->next = temp->next;
+		temp->next->prev = temp->prev;
+		free(temp);
+	}
+	else
+	{
+		printf("Index Out Of Bound\n"); //index is out of bound
+	}
 	return head;
 }
 
-void displayInReverse()
+void displayInReverse() //display the linked list in reverse order
 {
 	printf("the Linked List in Reverse Order is ");
-	struct node *temp = last;
+	struct node *temp = last; //creating iterator pointing to the last element
 	while (temp != NULL)
 	{
 		printf("%d ", temp->data);
@@ -126,10 +140,10 @@ void displayInReverse()
 	printf("\n\n");
 }
 
-void display()
+void display() //display the linked list
 {
 	printf("the Linked List is ");
-	struct node *temp = head;
+	struct node *temp = head; //creating iterator pointing to the head
 	while (temp != NULL)
 	{
 		printf("%d ", temp->data);
@@ -141,31 +155,31 @@ void display()
 int main()
 {
 	struct node *root = NULL;
+	root = createNode(4); // creating the list
 
-	root = createNode( 4);
-
-	additionOfNodeAtBeginning(6);
-	additionOfNodeAtEnding(90);
+	additionOfNodeAtBeginning(6); //adding the value 6 at beginning
+	additionOfNodeAtEnding(90);	  //adding value 90 at last
 	printf("After adding 90 at last ,");
-	display();
-	additionOfNodeAtRandomeIndex(12,1);
+	display(); //display the list
+	//index are starting from 0
+	additionOfNodeAtRandomeIndex(12, 1); //adding 12 at index 1
 	printf("After adding 12 at index 1 ,");
 	display();
 	additionOfNodeAtBeginning(1);
 	additionOfNodeAtEnding(2);
 	additionOfNodeAtBeginning(5);
 	additionOfNodeAtEnding(98);
-	additionOfNodeAtRandomeIndex(122,2);
+	additionOfNodeAtRandomeIndex(122, 2); //index are starting from 0
 	display();
-	deletingFromBeginning();
+	deletingFromBeginning(); //deleting the head element
 	printf("After Deletion from beginning, ");
 	display();
-	deletingFromEnding();
+	deletingFromEnding(); //deleting the last element from the list
 	printf("After deleting from end, ");
 	display();
-	deletingFromRandomIndex(3);
+	deletingFromRandomIndex(3); //deleting the element at index 3(0 is starting index)
 	printf("After deleting from index 3 ,");
 	display();
 
-	displayInReverse();
+	displayInReverse(); //display the linked list in reverse order
 }