INFSCI 0015 Data Structures Lecture 20: Linear Lists

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INFSCI 0015 - Data StructuresLecture 20 Linear
Lists

• Peter Brusilovsky
• http//www2.sis.pitt.edu/peterb/0015-011/

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From Data to Data Structures
machine level data storage
0100110001101001010001
primitive data types
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3.1415
'A'
array
structure
basic data structures
high-level data structures
stack
queue
list
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Some Data Structures
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Linear list

• A sequence of elements
• There is first and last element
• Each element has previous and next
• Nothing before first
• Nothing after last

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What makes a special kind of list

• What we can do with a linear list?
• Delete element
• Insert element
• Find element
• Traverse list
• Is the list sorted or not?
• Numerically
• Alphabetically
• Any other way

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Some classification of lists
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Insert list, data ? new list
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Retrieve list, criteria ? element
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Delete list, criteria ? new list
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Traverse list ? elements in order

• get_first(list) -
• returns first element if it exists
• get_next(list) -
• returns next element if it exists
• Both functions return NULL otherwise
• Calling get_next in a loop we will get one by one
  all elements of the list

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How we can implement a list?

• Array?
• Search is easy (sequential or binary)
• Traversal is easy
• for(i first i lt last i)
• process(ai)
• Insert and delete is not easy
• a good part of the array has to be moved!
• Hard to guess the size of an array

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A linked list implementation

• Linked list is a chain of elements
• Each element has data part and link part pointing
  to the next element

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A Node - an element of the LL
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Head and Node are Structures

• We need to define two structures one for a list
  head, one for a list node

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Head and Node simple int list
head
count

• struct intlist
• struct node head
• int count
• struct node
• int data
• struct node link

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data
link
99
data
link
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Head and Node name list

• struct intlist
• struct node head
• int count
• struct node
• char name
• struct node link

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Head and Node structure as data

• struct intlist
• struct node head
• int count
• struct node
• struct person data
• struct node link
• struct person
• char name
• int age

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Main operations

• Create list
• Add node
• beginning,middle or end
• Delete node
• beginning,middle or end
• Find node
• Traverse list

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Create list
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Add Empty list
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Add At the beginning of the list
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Add In the middle of the list
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Add At the end of the list
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Delete first
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Delete General case
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Traversing the list

• struct intlist mylist
• for(pWalker mylist.head
• pWalker ! NULL
• pWalker pWalker-gtlink)
• process(pWalker-gtdata)

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Traversing list as ADT

• We need an extra pointer to store current
  position
• get_first will set pos head
• get_next will set pos pos-gtlink