1. Recall What is a Data Structure Very Fundamental Data Structures
Arrays
What Arrays are good for
What Arrays do poorly
Linked Lists
Singly Linked List
Add h/t, Remove h/t
Doubly Linked List
Add, Remove

2. Recall too Equivalence Shallow & Deep Cloning a data structure Stacks
Queues

3. Application: Round Robin Schedulers
We can implement a round robin scheduler using a queue Q by repeatedly performing the following steps:
e = Q.dequeue()
Service element e
Q.enqueue(e)
Queue
Dequeue
Enqueue
Shared Service
© 2014 Goodrich, Tamassia, Goldwasser

4. Lists ADT and Iterators
Presentation for use with the textbook Data Structures and
Algorithms in Java, 6 edition , by M. T. Goodrich, R. Tamassia,
and M. H. Goldwasser, Wiley, 2014 th
Lists ADT and Iterators
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 1

5. The java.util.List ADT
The java.util.List interface includes the following methods:
q  
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 2

6. Example A sequence of List operations: q
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 3

7. Array Lists An obvious choice for implementing the list ADT is
to use an array, A , where A[i] stores (a reference
to) the element with index i .
q  
With a representation based on an array A , the
get( i ) and set( i , e ) methods are easy to implement
by accessing A[i] (assuming i is a legitimate index).
q   A
0 1 2 i n
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 4

8. Insertion In an operation add( i , o), we need to make room
for the new element by shifting forward the n - i
elements A [ i ], …, A [ n - 1]
q  
In the worst case ( i = 0), this takes O ( n ) time A
q  
0 1 2 i n A
0 1 2 i n A o
0 1 2 i n
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 5

9. Element Removal
In an operation remove (i), we need to fill the hole left by
the removed element by shifting backward the n - i - 1
elements A [ i + 1], …, A [ n - 1]
q  
In the worst case ( i = 0), this takes O ( n ) time
q   A o
0 1 2 i n A
0 1 2 i n A
0 1 2 i n
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 6

10. Performance In an array-based implementation of a dynamic list:
q  
The space used by the data structure is O ( n )
Indexing the element at i takes O (1) time
add and remove run in O ( n ) time
n  
n  
n  
In an add operation, when the array is full,
instead of throwing an exception, we can
replace the array with a larger one …
q  
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 7

11. Java Implementation © 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 8

12. Java Implementation, 2 © 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 9

13. Growable Array-based Array List
Let push(o) be the operation
that adds element o at the
end of the list
q  
Algorithm push ( o)
if t = S.length - 1 then
A ← new array of
When the array is full, we
replace the array with a
larger one
q  
size …
for i ← 0 to n -1 do
A [ i ] ← S [ i ]
How large should the new
array be?
S ← A
q  
n ← n +1
S [ n -1] ← o
n   Incremental strategy : increase
the size by a constant c
Doubling strategy : double the
n  
size
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 10

14. Growable Array-based Array List
Algorithm push ( o)
if t = S.length - 1 then
A ← new array of
size …
for i ← 0 to n -1 do
A [ i ] ← S [ i ]
S ← A
n ← n +1
S [ n -1] ← o
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 10

15. Positional Lists To provide for a general abstraction of a sequence of
elements with the ability to identify the location of an
element, we define a positional list ADT.
q  
A position acts as a marker or token within the
broader positional list.
q  
A position p is unaffected by changes elsewhere in a
list; the only way in which a position becomes invalid
is if an explicit command is issued to delete it.
q  
A position instance is a simple object, supporting only
the following method:
q  
P.getElement( ): Return the element stored at position p.
n  
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Lists and Iterators 11

16. Positional List ADT Accessor methods: q
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 12

17. Positional List ADT, 2 Update methods: q
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 13

18. Example A sequence of Positional List operations: q
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Lists and Iterators 14

19. Positional List Implementation
q   The most natural way
to implement a
positional list is with a
doubly-linked list.
prev
next
element
node
trailer
header
nodes/positions
elements
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 15

20. Insertion p A B C p q A B C X p q A B X C
Insert a new node, q, between p and its successor.
q   p A B C p q A B C X p q A B X C
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 16

21. Deletion p A B C D A B C p D A B C
Remove a node, p, from a doubly-linked list.
q   p A B C D A B C p D A B C
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Lists and Iterators 17

22. Iterators that abstracts the process of scanning
q   An iterator is a software design pattern
that abstracts the process of scanning
through a sequence of elements, one
element at a time.
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 18

23. The Iterable Interface
Java defines a parameterized interface, named
Iterable , that includes the following single method:
q  
iterator ( ): Returns an iterator of the elements in the
collection.
n  
An instance of a typical collection class in Java, such
as an ArrayList, is iterable (but not itself an iterator); it
produces an iterator for its collection as the return
value of the iterator ( ) method.
q  
Each call to iterator ( ) returns a new iterator instance,
thereby allowing multiple (even simultaneous)
traversals of a collection.
q  
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 19

24. The for-each Loop Java ’s Iterable class also plays a fundamental
role in support of the “for-each ” loop syntax:
q  
is equivalent to:
© 2014 Goodrich, Tamassia, Goldwasser
Lists and Iterators 20

25. The for-each Loop But to use remove you must : q
© 2014 Goodrich, Tamassia, Goldwasser 20

26. Implementing Iterators
Snapshot iterator
Lazy iterator
© 2014 Goodrich, Tamassia, Goldwasser

27. The Java Collections Framework
part of the java.util package
Children of Collection interface
© 2014 Goodrich, Tamassia, Goldwasser

28. The Java Collections Framework
© 2014 Goodrich, Tamassia, Goldwasser
Queues

29. See the book for List Iterators in Java
Java way Vs book way
List-Based Algorithms in the Java Collections Framework
© 2014 Goodrich, Tamassia, Goldwasser

30. Reading [G] Section 7.1 and 7.2
[G] Do not read subsection yet. We will visit it later.
[G] Section 7.3
[G] Section 7.4
[G] Section 7.5
[G] Section 7.6 and subsection 7.7.1