Insert - General Case data structure EE 22024.ppt

April 16, 2025
April 16, 2025 Anna University, Chennai - 600 025
Anna University, Chennai - 600 025 1
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Insert - General Case
 In general case, new node is always inserted
between two nodes, which are already in the
list. Head and tail links are not updated in
this case.
 We need to know two nodes "Previous" and
"Next", between which we want to insert the
new node.
 This also can be done in two steps:
• Update link of the "previous" node, to point to the new
node.
• Update link of the new node, to point to the "next" node.

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Singly-linked List - Deletion
 There are four cases, which can occur while
removing the node.
 We have the same four situations, but the
order of algorithm actions is opposite.
 Notice, that removal algorithm includes the
disposal of the deleted node - unnecessary in
languages with automatic garbage collection
(Java).

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List has only one node
 When list has only
one node, that the
head points to the
same node as the
tail, the removal is
quite simple.
 Algorithm disposes
the node, pointed
by head (or tail)
and sets both head
and tail to NULL.

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Remove First
 In this case, first node (current head node) is
removed from the list.
 It can be done in two steps:
• Update head link to point to the node, next to the
head.
• Dispose removed node.

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Remove Last
 In this case, last node (current tail node) is
removed from the list. This operation is a bit
more tricky, than removing the first node,
because algorithm should find a node, which
is previous to the tail first.
 It can be done in three steps:
• Update tail link to point to the node, before the
tail. In order to find it, list should be traversed
first, beginning from the head.
• Set next link of the new tail to NULL.

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Remove - General Case
 In general case, node to be removed is
always located between two list nodes. Head
and tail links are not updated in this case.
 We need to know two nodes "Previous" and
"Next", of the node which we want to delete.
 Such a removal can be done in two steps:
• Update next link of the previous node, to point to
the next node, relative to the removed node.

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Advantages of Using Linked Lists
 Need to know where the first node is
• the rest of the nodes can be accessed
 No need to move the elements in the list
for insertion and deletion operations
 No memory waste

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Cursor Implementation
Problems with linked list implementation:
 Same language do not support pointers!
• Then how can you use linked lists ?
 new and free operations are slow
• Actually not constant time
 SOLUTION: Implement linked list on an array -
called CURSOR

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Cursor Implementation - Diagram

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Cursor Implementation
If L = 5, then L represents list (A, B, E)
If M = 3, then M represents list (C, D, F)

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Arrays - Pros and Cons
 Pros
• Directly supported by C
• Provides random access
 Cons
• Size determined at compile time
• Inserting and deleting elements is
time consuming

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Linked Lists - Pros and Cons
 Pros
• Size determined during runtime
• Inserting and deleting elements is
quick
 Cons
• No random access
• User must provide programming
support

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Application of Lists
 Lists can be used
 To store the records sequentially
 For creation of stacks and queues
 For polynomial handling
 To maintain the sequence of operations
for do / undo in software
 To keep track of the history of web sites
visited

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Why Doubly Linked List ?
 given only the pointer location, we cannot access its
predecessor in the list.
 Another task that is difficult to perform on a linear
linked list is traversing the list in reverse.
 Doubly linked list A linked list in which each node is
linked to both its successor and its predecessor
 In such a case, where we need to access the node
that precedes a given node, a doubly linked list is
useful.

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Doubly Linked List
 In a doubly linked list, the nodes are linked
in both directions. Each node of a doubly
linked list contains three parts:
• Info: the data stored in the node
• Next: the pointer to the following node
• Back: the pointer to the preceding node

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Operations on Doubly Linked Lists
 The algorithms for the insertion and deletion
operations on a doubly linked list are
somewhat more complicated than the
corresponding operations on a singly linked
list.
 The reason is clear: There are more pointers
to keep track of in a doubly linked list.

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Inserting Item
 As an example, consider the Inserting an
item.
 To link the new node, after a given node, in
a singly linked list, we need to change two
pointers:
• newNode->next and
• location->next.
 The same operation on a doubly linked list
requires four pointer changes.

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Singly Linked List Insertion

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Doubly Linked List Insertion

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The Order is Important

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Doubly Linked List - Deletion
 One useful feature of a doubly linked list is
its elimination of the need for a pointer to a
node's predecessor to delete the node.
 Through the back member, we can alter the
next member of the preceding node to make
it jump over the unwanted node.
 Then we make the back pointer of the
succeeding node point to the preceding node.

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Doubly Linked List - Deletion

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Special Cases of Deletion
 We do, however, have to be careful about
the end cases:
• If location->back is NULL, we are deleting the
first node
• if location->next is NULL, we are deleting the last
node.
• If both location->back and location->next are
NULL, we are deleting the only node.

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Interaction

Insert - General Case data structure EE 22024.ppt

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Insert - General Case data structure EE 22024.ppt