Linked Lists

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Linked Lists
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Types of Linked Lists

• Singly-linked list
• Doubly-linked list
• Singly, circularly-linked list
• Doubly, circularly-linked list

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Singly-linked List
data
head pointer
head node
tail
Some refer to only the last node as the tail
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Doubly-linked List
data
head pointer
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Singly, Circularly-linked List
data
head pointer
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Doubly, Circularly-linked List
data
head pointer
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Singly-linked List in OO
other private data members
data object
list object
nodeobject
May include maximum number of nodes, current
number of nodes, or other items.
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A Look at Common Operations on a Singly-linked
List

• Locating an item
• Inserting an item
• Removing an item

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Locating an Item
Other Private Data members
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Locating an Item (cont)

• Design Decision
• What do we do if the item is not in the list?
• Performance
• What is the best case performance?
• What is the worst case performance?
• What is the average performance?
• How is the performance different in a sorted
  linked list (best, worst, average cases)?
• Sorted or unsorted, would the performance be
  better if the list were doubly-linked?

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Inserting an Item
Insert 17 at the head
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Inserting an Item (cont)
Insert 17 in sorted order
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Inserting an Item (cont)
In general, with a sorted list, there are three
cases - insert as first node - insert as
last node - insert somewhere in between
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Inserting an Item (cont)

• Design Decision
• What do we do if duplicates are not allowed?
• Performance
• If the list is not maintained in sorted order, it
  is most efficient to insert at the head.
• What is the asymptotic performance of this kind
  of insert?
• If we choose to insert at the end of the list,
  what is the asymptotic performance?

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Inserting an Item (cont)

• If the list is maintained in sorted order, we
  must search to find the proper place in the list,
  then insert.
• What is the asymptotic performance of this
  insert?
• Would performance be better if the list were
  doubly-linked?

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Removing an Item
Other Private Data members
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Three cases - remove first item - remove
last item - remove an item in between
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Removing an Item (cont)
How does the algorithm change if we use a
doubly-linked list?
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Removing an Item (cont)

• Design decisions
• What do we do if the item we are asked to delete
  is not in the list?
• What do we do if duplicates are allowed in the
  list?
• Performance
• Would performance be better if the list were
  doubly-linked?