Download Lists, Sequences, and Iterators

Iterators, Lists, and Sequences
Data Structures and Algorithms
CS 244
Brent M. Dingle, Ph.D.
Department of Mathematics, Statistics, and Computer Science
University of Wisconsin – Stout
Based on the book: Data Structures and Algorithms in C++ (Goodrich, Tamassia, Mount)
Some content from Data Structures Using C++ (D.S. Malik)
Points of Note
• Check assignment due dates
• HW08 due April 3 (today)
• HW09 due April 10
Last Time
• Last class we talked about
• Linked Lists
• Dynamic Arrays
• Book’s Vector ADT
• The Vector ADT (§6.1.1)
• Array-based implementation (§6.1.2)
• Stacks
• Queues
• Dequeues
Today
• Review: Iterators
• Iterators (§6.2.5)
 mostly FYI
• Lists and Sequences as ADTs
• Position ADT (§6.2.1)  mostly FYI
• List ADT (§6.2.2)
• Sequence ADT (§6.3.1)
• Sorting
Iterators
• Some functions supported by STL containers such as:
– begin(), end()
– return iterators to beginning or end of container
– insert(I,e)
– insert e just before the position indicated by iterator I
– analogous to our linked list operation: insertBefore(p)
– erase(I)
– removes the element at the position indicated by I
– analogous to our linked list operation: remove(p)
• The functions can be used to insert/remove elements from
arbitrary positions in the STL vector and list
Iterators Example
• In the previous class there was an exercise that was
based on the code:
• Located at or near something like:
• ContentUnit2InClassExamplesEx225_DequeWithIters.cpp
• Code example from this follows next slide
Iterator Example
// typedef deque< char > myDequeType;
myDeque.push_back(
myDeque.push_back(
myDeque.push_back(
myDeque.push_back(
myDeque.push_back(
'H' );
'O' );
'W' );
'D' );
'Y' );
//--------------------------------------------------------------------// Change them back but this time use iterators
// instead of reference pointers.
// Note how we dereference the iterators with * when setting them.
myDequeType::iterator it_begin = myDeque.begin();
myDequeType::iterator it_end = myDeque.end();
*it_begin = 'H'; // Change the first element from h back to H
--it_end;
*it_end = 'Y'; // Change the last element from y to back to Y
Iterator Example 2
// typedef deque< char > myDequeType;
void printContents( myDequeType deque )
{
//--------------------------------------------------------------------// Using iterators,
// which point to the beginning and ending of the vector,
// loop through the vector and print out its contents
myDequeType::iterator it_begin = deque.begin();
myDequeType::iterator it_end = deque.end();
cout << "Contents of myDeque: ";
}
while (it_begin != it_end )
{
cout << *it_begin << " " ;
++it_begin
}
cout << endl;
Group Class Activity
• Create a program that instantiates a vector of integers using
std::vector
• Then using a loop
• Based on iterators begin() and end()
• Pushes the Fibonacci numbers into the vector object
• 1 1 2 3 5…
• Starter Code can be found on D2L Circa:
• Unit2InClassExamples
• GCA210_VectorIterators.tar.gz
• Submit the code to the correct
D2L dropbox
• 1 submission per “group”
• Put all group member names
in comments at top of main CPP file
Forward and Backward
Lists and Sequences
FYI Background: Position ADT
• The Position ADT models the notion of place within a data structure
where a single object is stored
– often in the sense of relative position
• such as A is before B, or Z is after Y
– also in the sense of first, second, third, … last
• rather than just at index i
• A special null position refers to no object.
• Positions provide a unified view of diverse ways of storing data
– a cell of an array
– a node of a linked list
• Member functions:
– Object& element(): returns the element stored at this position
– bool isNull(): returns true if this is a null position
Book’s List ADT (§6.2.2)
• The List ADT models a
sequence of positions
storing arbitrary objects
– establishes a before/after
relation between positions
• It allows for insertion and
removal in the “middle”
• Query methods:
– isFirst(p), isLast(p)
• Generic methods:
– size(), isEmpty()
• Accessor methods:
– first(), last()
– before(p), after(p)
• Update methods:
– replaceElement(p, o),
swapElements(p, q)
– insertBefore(p, o),
insertAfter(p, o),
– insertFirst(o), insertLast(o)
– remove(p)
List ADT
• Query methods:
– isFirst(p), isLast(p) :
• return boolean indicating if the given position is the first or last,
respectively.
• Accessor methods
– first(), last():
• return the position of the first or last, resp., element of S
• an error occurs if S is empty
S is the list
– before(p), after(p):
• return the position of the element of S preceding or following,
respectively, the one at position p
• an error occurs if S is empty, or p is the first or last, resp., position
List ADT
• Update Methods
• replaceElement(p, o)
• Replace the element at position p with e
• swapElements(p, q)
• Swap the elements stored at positions p & q
• insertBefore(p, o), insertAfter(p, o),
• Insert a new element o into S before or after, resp., position p
• Output: position of the newly inserted element
• insertFirst(o), insertLast(o)
• Insert a new element o into S as the first or last, resp., element
• Output: position of the newly inserted element
• remove(p)
• Remove the element at position p from S
S is the list
Class Exercises Follow
• You are about to see 2 exercises
• Mostly a compare and contrast exercise set
• Think about run times too
• This is a group discussion activity
• Elect someone in your group to capture what is talked
about in a MS-Word or text document
• Randomly selected groups will present their findings at
conclusion of each exercise
Exercise 1 of 2
• Describe how to implement the following list ADT
operations using a singly-linked list
• list ADT operations: first(), last(), before(p), after(p)
• For each operation, explain how it is implemented and provide the
running time
next
• A singly linked list consists of
a sequence of nodes
• Each node stores
• element
• link to the next node
elem
head
node
tail

Leonard
Sheldon
Howard
Raj
Exercise 2 of 2
• Describe how to implement the following list ADT
operations using a doubly-linked list
– list ADT operations: first(), last(), before(p), after(p)
– For each operation, explain how it is implemented
and provide the running time
• Doubly-Linked List Nodes
implement Position and store:
• element
• link to previous node
• link to next node
next
prev
elem
• Special head/tail nodes
node
tail
head


Leonard
Sheldon
Howard
Raj
Enhanced Version
Solution: Singly Linked List
• In the implementation of the List ADT by means of a
singly linked list
•
•
•
•
The space used by a list with n elements is O(n)
The space used by each position of the list is O(1)
The before() operation runs in O(n) time
All the other operations of the List ADT run in O(1) time
Enhanced Version
Solution: Doubly Linked List
• In the implementation of the List ADT by means of a
doubly linked list
• The space used by a list with n elements is O(n)
• The space used by each position of the list is O(1)
• All the operations of the List ADT run in O(1) time
Variances of Implementation
• The details of implementing a list will vary
• So STL implementation does not always match the
book’s described ADT
• This is common
• So always check the interface description
• wherever you may work
List Summary
• List Operation Complexity for different implementations
List Singly-Linked
List Doubly- Linked
first(), last(), after(p)
insertAfter(p,o),
replaceElement(p,o),
swapElements(p,q)
O(1)
O(1)
before(p),
insertBefore(p,o),
remove(p)
O(n)
O(1)
Size(), isEmpty()
O(1)
O(1)
Sequence ADT
• The Sequence ADT is the union of • List-based methods:
the Vector and List ADTs
– first(), last(), before(p),
• Elements accessed by
after(p),
– Rank, or
replaceElement(p, o),
– Position
swapElements(p, q),
• Generic methods:
insertBefore(p, o),
– size(), isEmpty()
insertAfter(p, o),
• Vector-based methods:
insertFirst(o),
– elemAtRank(r), replaceAtRank(r,
insertLast(o), remove(p)
o), insertAtRank(r, o),
removeAtRank(r)
• Bridge methods:
– atRank(r), rankOf(p)
Applications of Sequences
• The Sequence ADT is a basic, general-purpose,
data structure for storing an ordered collection of
elements
• Direct applications:
• Generic replacement for stack, queue, vector, or list
• small database (e.g., address book)
• Indirect applications:
• Building block of more complex data structures
Sequence Implementations
Operation
size, isEmpty
atRank, rankOf, elemAtRank
first, last, before, after
replaceElement, swapElements
replaceAtRank
insertAtRank, removeAtRank
insertFirst, insertLast
insertAfter, insertBefore
remove
Array
1
1
1
1
1
n
1
n
n
List
1
n
1
1
n
n
1
1
1
Outline and Reading
• Where we are headed
• Bubble Sort (§6.4)
• Merge Sort (§11.1)
• Summary of sorting algorithms
The End of This Part
• Next
• Bubble Sort and Merge Sort
• Chapter 6 and 11.1