Linked List - Insertion & Deletion

Linked List - Insertion & Deletion

• 1.
  Linked List -Insertion & Deletion Prepared by: Afaq Mansoor Khan BSSE III- Group A Session 2017-21 IMSciences, Peshawar.
• 2.
  Last Lecture Summary •Dynamic Memory Allocation ▫ New Operator ▫ Delete Operator ▫ Heap ▫ dot . and -> operators • Introduction to Linked List ▫ Types ▫ Advantages ▫ Disadvantages ▫ Applications ▫ Difference between Array and Linked List
• 3.
  Objectives Overview • Insertionin Linked List with following criteria ▫ Start of the list ▫ End of the list ▫ Middle of the list ▫ Anywhere in the list • Deletion of a node from ▫ The Tail of the List ▫ The Head of the List ▫ A desired location in the list ▫ Delete node with a particular value
• 4.
  Insertion in LinkedList
• 5.
  Insertion A Node inthe Linked List can be inserted at: 1. Beginning of the list. 2. End of the list. 3. Middle of the list 4. Anywhere in the list
• 6.
  Insertion at theBeginning - Algorithm Steps to insert a Node at beginning : 1. Allocate a new node 2. Insert new element 3. Have new node point to old head 4. Update head to point to new node
• 8.
  Implementation • int LinkedList:: addAtFront(node *n) { • int i = 0; • //making the next of the new Node point to Head • n->next = head; • //making the new Node as Head • head = n; • i++; • //returning the position where Node is added • return i; • }
• 9.
  Insertion at theEnd - Algorithm Steps to insert a Node at End: 1. Allocate a new node 2. Insert new element 3. Have new node point to null 4. Have old last node point to new node 5. Update tail to point to new node
• 11.
  Implementation • int LinkedList:: addAtEnd(node *n) { • if(head == NULL) { //If list is empty • head = n; //making the new Node as Head • n->next = NULL; //making the next pointe of the new Node as Null • } • else { • node *n2 = getLastNode(); //getting the last node • n2->next = n; } } • node* LinkedList :: getLastNode() { • node* ptr = head; //creating a pointer pointing to Head • //Iterating over the list till the node whose Next pointer points to null • //Return that node, because that will be the last node. • while(ptr->next!=NULL) { • //if Next is not Null, take the pointer one step forward • ptr = ptr->next; } • return ptr; }
• 12.
  Insertion at theMiddle - Algorithm Steps to insert a Node at Middle: 1. Allocate a new node 2. Insert new element 3. Go to node that should follow the one to add 4. Have that node point to the new node 5. Have new node point to node next node to the found node.
• 17.
  Insertion at aSpecific Position - Algorithm Steps to insert a Node at Specified Position: 1. Traverse the Linked list up to position-1 nodes. 2. Once all the position-1 nodes are traversed, allocate memory and the given data to the new node. 3. Point the next pointer of the new node to the next of current node. 4. Point the next pointer of current node to the new node.
• 18.
  Implementation • // functionto insert a Node at required postion • void insertPos(Node** current, int pos, int data) • { • if (pos < 1 || pos > size + 1) • cout << "Invalid postion!" << endl; • else { • while (pos--) { • if (pos == 0) { • Node* temp = getNode(data); • temp->next = *current; • *current = temp; • } • else • current = &(*current)->next; • } • size++; • } • }
• 19.
  Deletion from LinkedList
• 20.
  Deletion A node inthe linked list can be Deleted from: 1. The Tail of the List 2. The Head of the List 3. A Desired location in the list 4. Delete node with a particular value
• 21.
  Deletion at theBeginning - Algorithm Steps: 1. Store Current Start in Another Temporary Pointer 2. Move Start Pointer One position Ahead 3. Delete temp i.e. Previous Starting Node as we have Updated Version of Start Pointer
• 25.
  Implementation • Node *removeFirstNode(struct Node* head) • { • if (head == NULL) • return NULL; • • // Move the head pointer to the next node • Node *temp = head; • head = head->next; • • delete temp; • • return head; • }
• 26.
  Deletion at theEnd - Algorithm Steps to Delete a Node at End : 1. Step 1: If FIRST = NULL then Write “Linked List is Empty” 2. Step 2: If FIRST->LINK = NULL then Return FIRST->INFO FIRST=NULL Else SAVE=FIRST Repeat while SAVE->LINK ≠ NULL PRED=SAVE SAVE=SAVE->LINK Return SAVE->INFO PRED->LINK=NULL 3. Step 3: Exit
• 28.
  Implementation • Node* removeLastNode(structNode* head) • { • if (head == NULL) • return NULL; • • if (head->next == NULL) • { • delete head; • return NULL; • } • • // Find the second last node • Node* second_last = head; • while (second_last->next->next != NULL) • second_last = second_last->next; • • // Delete last node • delete (second_last->next); • • // Change next of second last • second_last->next = NULL; • • return head; • }
• 29.
  Deletion at aDesired Location - Algorithm Steps: 1. If start =NULL 2. Print”over flow” 3. Return 4. End if 5. Set ptr=start 6. Assign value=start -> info 7. Set start=start -> next(second node becomes the first node). 8. Release the node pointed by ptr to the memory heap. 9. Exit.
• 31.
  Implementation • void deleteNode(structNode **head_ref, int position) • { • if (*head_ref == NULL) // If linked list is empty • return; • struct Node* temp = *head_ref; // Store head node • • if (position == 0) // If head needs to be removed • { • *head_ref = temp->next; // Change head • free(temp); // free old head • return; • } • for (int i=0; temp!=NULL && i<position-1; i++) // Find previous node of the node to be deleted • temp = temp->next; • if (temp == NULL || temp->next == NULL) // If position is more than number of Nodes • return; • • // Node temp->next is the node to be deleted • // Store pointer to the next of node to be deleted • struct Node *next = temp->next->next; • • // Unlink the node from linked list • free(temp->next); // Free memory • • temp->next = next; // Unlink the deleted node from list • }
• 32.
  Delete Node witha Particular Value - Algorithm Steps: 1. Store address of head in a double pointer till we find a non “key” node. This takes care of the 1st while loop to handle the special case of the head. 2. If a node is not “key” node then store the address of node->next in pp. 3. If we find a “key” node later on then change pp (ultimately node->next) to point to current node->next
• 34.
  Implementation • void deleteKey(structNode **head_ref, int key) • { • struct Node* temp = *head_ref, *prev; // Store head node • • • while (temp != NULL && temp->data == key) // If head node itself holds the key or multiple occurrences of key • { • *head_ref = temp->next; // Changed head • free(temp); // free old head • temp = *head_ref; // Change Temp • } • • while (temp != NULL) // Delete occurrences other than head • { • // Search for the key to be deleted, keep track of the • // previous node as we need to change 'prev->next' • while (temp != NULL && temp->data != key) • { • prev = temp; • temp = temp->next; • } • • if (temp == NULL) return; // If key was not present in linked list • • prev->next = temp->next; // Unlink the node from linked list • • free(temp); // Free memory • • temp = prev->next; //Update Temp for next iteration of outer loop • } • }
• 35.
  Summary • Insertion inLinked List with following criteria ▫ Start of the list ▫ End of the list ▫ Middle of the list ▫ Anywhere in the list • Deletion of a node from ▫ The Tail of the List ▫ The Head of the List ▫ A desired location in the list ▫ Delete node with a particular value
• 36.
  References • https://www.studytonight.com/data- structures/linear-linked-list • https://www.codelike.in/c/linked-list/ •http://www.c4learn.com/data-structure • https://www.slideshare.net/swajahatr/linked-list-c • http://www.thecodegallery.com/DSM/DeleteLast.ph p • https://www.slideshare.net/sathasivamr1/team-7- 42605180