Linked Structures

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Linked Structures

• Computer Science and Engineering

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Linked List

• We will study
• The concept of linked structure (list)
• Java Linked list
• State design pattern-based realization of a
  linked list

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Consider an Array

• Array is fixed size (non-mutable, static)
• Array insert is difficult
• Default indexing 0..n-1, predefined sequence of
  elements
• Allows random access

Insert here

N-1
0 1 2 3 4
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Linked List

• A linked list is an empty list or collection of a
  number of nodes, each containing one data element
  and one (or more) links to other nodes.
• Linked lists permit dynamic insertion and removal
  of nodes at any point in the list. Linked lists
  do not allow random access.
• The simplest kind of linked list is a singly
  linked list, which has one link per node. This
  link points to the next node in the list, or to a
  null value if it is the last node. This kind of
  list allows sequential access to elements.
• It is used where the size and structure of the
  data needs to be flexible and dynamic.

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Varieties of Linked List

• Simple linked list
• Linked list with special node(s) for head and/or
  tail
• Null terminator
• Sentinel as terminator
• Single link, double link, multi-link, circular
  linked
• Pointer to first and last node

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A node of linked list
public class Node Object item Node
next some times you have explicit
representation for a head and or tail.
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Node Class
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Linked List Operations

• Construct
• Insert (first, last, anywhere)
• Delete (first, last, anywhere)
• Size
• Search for an item
• Process Traverse, iterate to do something

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JDK1.4 Linked List
Object
AbstractCollection
Collection
AbstractList
List
AbstractSequentialList
List, java.io.Serializable, java.lang.Cloneable
LinkedList
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LinkedLists inheritance and related classes

• Most of the linked list functionality is
  specified in the interface List.
• Serializable defines the disk archiving (object
  read/write) functionality.
• Cloneable defines the cloning ability.
• LinkedList class defines the variables needed for
  storing the header and size.
• A ListIterator class offers the Iterator facility.

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Linked List class
//constructors add (index I, Object o) //
inserts add(Object o) //appends addFirst(Object
o) addLast(Object o) Object remove(index
i) boolean remove(Object o) Object
removeFirst() Object removeLast() Object
get(index i) Object getFirst() Object
getLast() Object set(index i, Object o) returns
replaced Object
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Linked List Class (contd.)
ListIerator listIterator(index i) boolean
contains(Object o) clear() int indexOf(Object
o) int lastIndexOf(Object o) // first
occurrence or 1 Object toarray() int size()
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(No Transcript)
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java.util.LinkedList Empty List
object
header
Doubly linked list with a special node
header. For an empty list all three fields point
to the header itself
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Java.util.LinkedList Non-Empty List
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remove(Object o)

• Locate the Entry e with Object o (Object can be
  null).
• If no such Entry throw an exception.
• Update pointers
• 3.1 Update previous entrys next to es next
• 3.2 Update es nexts previous to es previous
• 3.3 update size size size 1

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Remove an entry
Step 3.2
Step 3.1
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Remove an entry
Header
Step 2
Object
Object
Object
Entry e
Step 1
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Java Code for Step 3 of remove

• e.previous.next e.next //3.1
• e.next.previous e.previous //3.2
• size-- //3.3

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add(int index, Object o)

• Inserts an Entry of Object o before Entry at the
  given index.
• Retrieve the Entry e at the given index.
• Construct an Entry out of Object o and add it
  before e
• 2.1 Construct Entry x with o as Object, e as
  next and e.previous as previous.
• 2.2 Update next pointer of xs previous Entry
• 2.3 Update previous pointer of xs next Entry.
• 2.4 size

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add(int index, Object o) Step 2
Entry e at given index
Entry x
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add(int index, Object o) Step 2

• Let e be the entry at the given index.
• Entry x new Entry(o, e, e.previous) //step 2.1
• x.previous.next x //step 2.2
• x.next.previous x //step 2.3
• size

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add(int index, Object o) Step 2
header
Object
Object
Object
Entry e at given index
2.2
2.3
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Iterator Pattern

• When you want to access elements of a collection
  sequentially without the knowledge of the
  underlying representation.
• Ex 1 MineSweeper surroundIterator that presents
  you list of all valid surrounding cells (0-8) for
  sequential access
• Ex 2 Maze sequence of valid neighbors
• Ex 3 winterMonths sequence of all winter months
  from a list of all months can be defined for
  polymorphic dispatch for various types of
  geographic zones
• A simple iterator interface hasNext(), next(),
  hasPrevious(), previous(), currentElem()

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Java Linked List Iterator

• Implemented as an inner class.
• Review an inner class is a class embedded within
  another class. Scope is limited to the embedding
  class.
• In fact, LinkedList has two inner classes
  ListItr and Entry.
• A listIterator(int index) index specifies the
  starting point in the list for generating the
  elements of the iterator. You may request a
  partial list Iterator.

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Using a List

• Problem Make a list of all routes in city map.
• class Route int origin
• int dest
• Route (int a, int b)
• LinkedList map new LinkedList()
• map.add( route(23,45))
• etc.
• //print me a list of all train routes
• // assume a trainIterator is available
• //think about the implementation of trainIterator

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Using an Iterator

• // generate the iterator
• ListIterator tR map.trainIterator()
• while (tr.hasNext())
• System.out.println(tr.next())