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Linked Lists

Linked Lists. Introduction. In linked list each item is embedded in a link Each item has two parts Data Pointer to the next item in the list Insert, Delete and Edit operations can be performed Each item of the list can only be accessed through the next pointer, unlike arrays.

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Linked Lists

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  1. Linked Lists

  2. Introduction • In linked list each item is embedded in a link • Each item has two parts • Data • Pointer to the next item in the list • Insert, Delete and Edit operations can be performed • Each item of the list can only be accessed through the next pointer, unlike arrays

  3. Graphical Representation Item 1 Item 4 Item 2 Item 3 Front Data Next Null

  4. Differences between Linked Lists and Arrays • The order of linked items maybe different than the physical storage of the items • Linked Lists only allow sequential access as compared to random access in arrays

  5. Types of Linked ListsSingly-Linked Lists • Simplest kind of linked lists • One link per node • The link points to only the next item in the list 45 21 34 NULL A singly linked list, contains two values – value of the current node and a pointer to the next node

  6. Doubly Linked Lists • Doubly-Linked List or two-way linked list • Each node has a data value and two links, One pointing to the next item and second pointing to the previous item NULL 12 67 78 NULL

  7. Circularly Linked Lists • The first and last nodes are linked together • Circular linked lists can be implemented for both the singly and doubly linked lists • Have no start of end • It is most useful in the cases where you have one item and want to see all the items 45 21 34

  8. Application of Linked Lists • Used in implementing other data structures like, stacks and queues • In situations where the number of the items to be added is not known before hand • A lot of addition and deletion operations are performed • Position of the added items is important

  9. Linked Lists vs. Arrays • Advantages • Elements can be inserted into linked lists indefinitely, array will eventually either fill up or need to be resized, an expensive operation that may not even be possible if memory is fragmented • Deletion of items from linked lists does not leave the list with wasted memory unlike arrays • Useful in implementing persistent data structure • A persistent data structure always preserves its previous version when it is modified

  10. Linked Lists vs. Arrays (contd…) New Nodes Old Nodes • Disadvantages • Arrays allow random access Linked lists don’t • Singly linked lists can only be traversed in one direction • Sequential access on arrays is faster than linked lists due to not using next pointer NULL An example of persistent data structure using linked lists

  11. Josephus Problem • A good example to demonstrate the strengths and weaknesses of linked lists • The Josephus problem is an election method that works by having a group of people stand in a circle. • Starting at a predetermined person, you count around the circle n times. • Once you reach nth person, take them out of the circle and have the members close the circle. • Then count around the circle the same n times and repeat the process, until only one person is left. • That person wins the election.

  12. Josephus Problem (contd…) • All the people can be seen as a circular linked list • Deleting any item of the list is only rearranging of the next pointer, in arrays - an item has to be deleted and whole list should be resized • However finding the person will be a difficult task for linked list as it would a sequential search and needs to recurse through the list if person is not found. Whereas is arrays it would be very easy to find nth item of the array.

  13. Singly Linked List vs. Doubly Linked Lists • Doubly linked lists need more space per node • Doubly linked lists are easy to traverse as it allows traversal in both directions • Insert and delet operations on doubly linked lists are relatively easier, it only requires the address of the nodes to be operated on

  14. Circular vs. Linear Linked Lists • Circular linked lists are the most natural selection for implementing real world circular objects like people standing in circle • Circularly linked list allows transversal of the list starting from any point • Circularly linked lists allow quick access to first and last item. • Main disadvantage of circulary linked lists is its complex iteration.

  15. Inserting a New Item Item 1 Item 4 Item 2 Item 3 Front New Item Data Next Null

  16. Graphical Depiction Item 1 Item 4 Item 2 Item 3 Front Data Next Null

  17. Deleting an Item Item 1 Item 4 Item 2 Item 3 Front Data Next Null

  18. Typical Implementation • struct node { double data; node* next; }; • As this data structure points to its own type structure therefore its called “self referential” class node { private: double data; node* next; public: getnext(); addnode(node *n); deletenode(node *n); };

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