![Linked List Manipulation Algorithms
List Traversal
Let START be a pointer to a linked list in memory. Write an
algorithm to print the contents of each node of the list
Algorithm:
TRAVERSE(DATA, LINK, START)
1. set PTR = START
2. repeat step 3 and 4 while PTR ≠ NULL
3. print PTR->DATA
4. set PTR = PTR -> LINK
5. stop
1000
START
2000 3000 4000
PTR
PTR = LINK[PTR]
10 20 30 40
10 20 30 40 00
Data Link](https://image.slidesharecdn.com/ds4-linkedlists-180827163443/85/Data-Structure-and-Algorithms-Linked-List-9-320.jpg)
![Search for an Item
Search for an ITEM
Let START be a pointer to a linked list in memory. Write an
algorithm that finds the location LOC of the node where ITEM first
appears in the list, or sets LOC=NULL if search is unsuccessful.
Algorithm:
SEARCH (DATA, LINK, START, ITEM, LOC)
1. set PTR = START
2. repeat step 3 while PTR ≠ NULL
3. if ITEM == PTR -> DATA, then
4. set LOC = PTR, and Exit
5. else
6. set PTR = PTR -> LINK
7. set LOC = NULL /*search unsuccessful */
8. Stop
1000
START
2000 3000 4000
PTR
PTR = LINK[PTR]](https://image.slidesharecdn.com/ds4-linkedlists-180827163443/85/Data-Structure-and-Algorithms-Linked-List-10-320.jpg)
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Data Structure and Algorithms Linked List
- 1. Introduction: memory representation, allocation and garbage collection. Operations: Traversal, insertion and deletion. Header linked lists: Grounded and Circular Two-way lists: operations on two way linked lists
- 2. Introduction Linked list Linear collection of self-referential class objects, called nodes Connected by pointer links Accessed via a pointer to the first node of the list Link pointer in the last node is set to null to mark the list’s end Use a linked list instead of an array when You have an unpredictable number of data elements You want to insert and delete quickly.
- 3. Self-Referential Structures Self-referential structures Structure that contains a pointer to a structure of the same type Can be linked together to form useful data structures such as lists, queues, stacks and trees Terminated with a NULL pointer (0) Diagram of two self-referential structure objects linked together struct node { int data; struct node *nextPtr; }; nextPtr Points to an object of type node Referred to as a link 100 NULL pointer (points to nothing)Data member and pointer 500… 3 2
- 4. Linked Lists Types of linked lists: Singly linked list Begins with a pointer to the first node Terminates with a null pointer Only traversed in one direction Circular, singly linked Pointer in the last node points back to the first node Doubly linked list Two “start pointers” – first element and last element Each node has a forward pointer and a backward pointer Allows traversals both forwards and backwards Circular, doubly linked list Forward pointer of the last node points to the first node and backward pointer of the first node points to the last node
- 5. Linked Representation of Data In a linked representation, data is not stored in a contiguous manner. Instead, data is stored at random locations and the current data location provides the information regarding the location of the next data. Adding item 498 on to the linked list Q: What is the cost of adding an item? Q: how about adding 300 and 800 onto the linked list Deleting item 358 from the linked list Q: What is the cost of deleting an item? Q: What is the cost of searching for an item? 345 358 490 501 513 724 797 701 561 555 345 358 490 501 513 724 797 701 561 555 498 345 358 490 501 513 724 797 701 561 555 498
- 6. Linked List How do we represent a linked list in the memory Each location has two fields: Data Field and Pointer (Link) Field. Linked List Implementation struct node { int data; struct node *link; }; struct node my_node; Example: START Node Element Pointer (Link) Field Data Field Null Pointer 300 5 500 0 100 4 200 1 400 2 1 2 3 4 5 3 NULL
- 7. Conventions of Linked List There are several conventions for the link to indicate the end of the list. 1. a null link that points to no node (0 or NULL) 2. a dummy node that contains no item 3. a reference back to the first node, making it a circular list.
- 8. bat cat sat vat NULL
- 9. Linked List Manipulation Algorithms List Traversal Let START be a pointer to a linked list in memory. Write an algorithm to print the contents of each node of the list Algorithm: TRAVERSE(DATA, LINK, START) 1. set PTR = START 2. repeat step 3 and 4 while PTR ≠ NULL 3. print PTR->DATA 4. set PTR = PTR -> LINK 5. stop 1000 START 2000 3000 4000 PTR PTR = LINK[PTR] 10 20 30 40 10 20 30 40 00 Data Link
- 10. Search for an Item Search for an ITEM Let START be a pointer to a linked list in memory. Write an algorithm that finds the location LOC of the node where ITEM first appears in the list, or sets LOC=NULL if search is unsuccessful. Algorithm: SEARCH (DATA, LINK, START, ITEM, LOC) 1. set PTR = START 2. repeat step 3 while PTR ≠ NULL 3. if ITEM == PTR -> DATA, then 4. set LOC = PTR, and Exit 5. else 6. set PTR = PTR -> LINK 7. set LOC = NULL /*search unsuccessful */ 8. Stop 1000 START 2000 3000 4000 PTR PTR = LINK[PTR]
- 11. Insert an Item Insertion into a Listed List Let START be a pointer to a linked list in memory with successive nodes A and B. Write an algorithm to insert node N between nodes A and B. Algorithm: INSERT(DATA, LINK, START, A, B, N) 1. Set PTR = START 2. Repeat step 3 while PTR ≠ NULL 3. If PTR == A, then 4. Set N->LINK = PTR -> LINK (or = B) 5. Set PTR->LINK = N 6. exit 7. else 8. Set PTR=PTR->LINK 9. If PTR == NULL insertion unsuccessful 10. Stop START 1000 2000 3000 4000 5000 Node A Node B PTR START 1000 2000 3000 4000 5000 Node A Node B 3500 Node N 3 cases: first node, last node, in-between node. (ex: if ITEM = 500? if ITEM = 6000?)
- 12. Delete an Item Deletion from a Linked List Let START be a pointer to a linked list in memory that contains integer data. Write an algorithm to delete note which contains ITEM. Algorithm DELETE (DATA, LINK, START, ITEM) 1. Set PTR=START and TEMP = START 2. Repeat step 3 while PTR ≠ NULL 3. If PTR->DATA == ITEM, then 4. Set TEMP->LINK = PTR -> LINK, exit 5. else 6. TEMP = PTR 7. PTR = PTR -> LINK 8. Stop 3 cases: first node, last node, in-between node. (ex: if ITEM = 1000? if ITEM = 5000?) PTR START 1000 2000 3000 4000 5000 Node A Node B 3500 Node N START 1000 2000 3000 4000 5000 Node A Node B 3500 Node N 3500 ITEM ….. TEMP
- 13. Header Linked Lists Header linked list is a linked list which always contains a special node called the Header Node, at the beginning of the list. It has two types: a) Grounded Header List Last Node Contains the NULL Pointer b) Circular Header List Last Node Points Back to the Header Node 13 Header linked list Grounded Header linked list Circular Header linked list
- 14. Grounded Header Link List A grounded header list is a header list where the last node contains the null pointer. The term “grounded” comes from the fact that many texts use the electrical ground symbol to indicate the null pointer. Header Node Start Figure: Grounded Header Link List
- 15. Circular Header Linked List A circular header Link list is a header list where the last node points back to the header node. The chains do not indicate the last node and first node of the link list. In this case, external pointers provide a frame reference because last node of a circular link list does not contain null pointer. Header Node Figure: Circular Header Link List Start
- 16. Benefit of using Header Node One way to simplify insertion and deletion is never to insert an item before the first or after the last item and never to delete the first node You can set a header node at the beginning of the list containing a value smaller than the smallest value in the data set You can set a trailer node at the end of the list containing a value larger than the largest value in the data set. These two nodes, header and trailer, serve merely to simplify the insertion and deletion algorithms and are not part of the actual list. The actual list is between these two nodes.
- 17. Two-way lists A two-way list is a linear collection of data elements, called nodes, where each node N is divided into three parts: Information field Forward Link which points to the next node Backward Link which points to the previous node The starting address or the address of first node is stored in START / FIRST pointer . Another pointer can be used to traverse list from end. This pointer is called END or LAST.
- 18. Two-way lists(cont…) Every node (except the last node) contains the address of the next node, and every node (except the first node) contains the address of the previous node. A two-way list (doubly linked list) can be traversed in either direction.
- 19. Representations of Two-way lists Start X 4 2 10 Last INFO Field BACK Pointer FORE Pointer X
- 20. Thank You