©2006 Felleisen, Proulx, et. al.
In this problem set you will examine the properties of the different
algorithms we have seen as well as see and design new ones. The goal
is to learn to understand the tradeoffs between different ways of
writing the same program, and to learn some techniques that can be
used to explore the algorithm behavior.
To practice working with the ArrayList start by implementing
the selection sort. Because we will work with several
different sorting algorithms, yet want all of them to look the
same the selection sort will be a method in the class that
extends the abstract class ASortAlgo. A sorting algorithms
needs to be given the data to sort, the Comparator to use to
determine the ordering, and needs to provide an access to the data it
produces. Additionally, the ASort class also includes a field
that represents the name of the implementing sorting algorithm.
abstract class ASortAlgo<T> { /** the comparator that determines the ordering of the elements */ public Comparator<T> comp; /** the name of this sorting algorithm */ public String algoName; /** * Initialize a data set to be sorted * with the data generated by the traversal. * @param the given traversal */ abstract public void initData(Traversal<T> tr); /** * Sort the data set with respect to the given Comparator * and produce a traversal for the sorted data. * @return the traversal for the sorted data */ abstract public Traversal<T> sort(); }
Design the class ArrSortSelection that implements a
selection sort and extends the class ASortAlgo using an
ArrayList as the dataset to sort. The ArrayList
becomes an additional field in this class.
The initData initializes the ArrayList by
adding to it all the data generated by the given Traversal.
the new method selectionSort implements a mutating
selection sort on this ArrayList. There are numerous
lecture notes and labs from the past several years available
online that guide you through the design of selection
sort. The third part of you draft textbook has a
section on selection sort on pages 102-112.
The sort method invokes a selection sort on this
ArrayList and returns an instance of ALT the
Traversal over the data in an ArrayList.
Do this once you include the code in the main part of your assignment.
Include in the class a self test in the form of a
method testSort() that provides a test for all methods in
this class. There is an example of this technique in
the AListSortInsertion class provided with this homework.
Design the class ArrSortInsertion that implements a
mutating insertion sort for an ArrayList and extends the
class ASortAlgo in that same way as was done for the
selection sort.
You may work on this part with your partner if you wish -- or get any help you need. However, you must make sure that at the end you understand every part of the code and how the tests were designed.
We have seen by now three different ways to sort a collection of data: The insertion sort, the quicksort, and the binary tree sort.
The binary tree sort was hidden -- we first designed the method to insert data into a binary search tree, then we designed the traversal over the binary search tree that generated the elements in the desired order.
The algorithms all have the same purpose, yet they do not conform
to the same interface. They also deal with the data structured in
different ways. However, we would
like to compare these algorithms for efficiency (speed).
ASortAlgo class: Reporting the results
Our first task is to design wrappers for all these algorithms that will allows us to use them interchangeably to sort any collection of data supplied through an iterator. Of course, we want all of them to produce the data in a uniform format as well. Therefore, we want all of these algorithms to produce a traversal for the sorted list.
Because the traversal of a binary search tree involes quite a lot of
computation, to make to comparisons fari, we will conclude the binary
tree sort by producing an sorted ArrayList, generated by the
data produced by the traversal of the binary search tree we have
constructed.
ASortAlgo class: Initializing the data
The abstract class ASortAlgo introduced in the
Etudes provides a uniform
wrapper for all sorting algorithms. The initData
method consumes the given traversal for the data to be sorted and saves
the given data in a data structure appropriate for this algorithm.
For the algorithms that are based on the ArrayList the
initData method creates a new ArrayList and adds all
elements generated by the given Traversal. For the
AListSortInsertion class that implements the insertion sort
for a recursively built AList, the initData method
copied the given data into a new AList. For the quicksort
algorithm that is based on recuesively build lists, this will not be
necessary - as the algorithm traverses over the data and constructs
two new lists - the upper and the lower partition, and does not use
any properties of the lists. Finally, for the binary tree sort the
task of constructing the binary tree comprises a substantial amount of
work, and so should be done as a part of the sort
method. Therefore, the initData method just copies the
reference to the Traversal.
We provide an example of a class that implements the insertion sort
algorithm for data saved as AList<T>.
ASortAlgo class: Running the timing tests
To measure the time each algorithm takes to complete its task, we will
invoke each algorithm in three parts. First, we provide the data to
sort and invoke the initData method. Next we start the timer,
invoke the sort method and stop the timer when the method
returns the result. Finally, we check that the data was indeed sorted
and record the result.
We will test each of the several sorting algorithms on several
datasets (varying the dataset size and whether the data is in the
original order as received from the database, or is
randomized). For each dataset we will use several different
Comparators -- by name and state, by latitude, and by zip
code.
The results will be recorded in a uniform way, so that we may then look for patterns of behavior.
Here is a summary of the algorithms you will implement. Please, use the names given below:
ArrSortSelection -- done as a Part 1 of the Etudes
ArrSortInsertion -- done as Part 2 of the Etudes
AListSortInsertion -- provided
ABinaryTreeSort -- modify the solution to homework 5
AListSortQuickSort -- to be done (modify 8.1 part 9 of
homework 8)
ArrSortQuickSort -- to be done
Design the method in the Tests class that determines
whether the data generated by the given Traversal iterator is
sorted, with regard to the given Comparator.
Later, you will need the same method in the class TimerTests.
Complete the design the classes AListSortSelection and
AListSortInsertion.
Include in each class a self test in the form of a
method testSort(Tests tests) that provides a test for all
methods in this class.
Design the class ABinaryTreeSort that that extends the
ASortAlgo class. It performs the binary tree
sort on the data supplied by the Traversal iterator.
The sort method first builds the
binary search tree from the data provided by the iterator, then saves
the data generated by the inorder traversal in an ArrayList
or in an AListOfCities data structure.
Include in each class a self test in the form of a
method testSort(Tests tests) that provides a test for all
methods in this class.
Design the class AListSortQuickSort that performs the
recursively defined quicksort
on the data supplied by the Traversal iterator and producing
an AListOfCities data structure. You will need a helper
method to append two lists together.
HtDP has a good explanation of quicksort.
Include in each class a self test in the form of a
method testSort(Tests tests) that provides a test for all
methods in this class.
Design the class ArrSortQuickSort that that extends the
ASortAlgo class. It performs the quicksort
sort on an ArrayList. The ArrayList is initialized
from the data supplied by the Traversal iterator.
You may use any textbook or the web to find an implementation of this algorithm, but you are responsible for the correctness of your implementation.
Include in each class a self test in the form of a
method testSort(Tests tests) that provides a test for all
methods in this class.
Note: If you are having problems with this algorithm, go on to the Time Trials and finish this only if you have time left.
All of the tests we designed as the part of our code sorted only very small collections of data. It is important to make sure that the programs work well for large amounts of data as well. It is possible to estimate the amount of time an algorithm should take in comparison to others. However, we would like to verify these results on real data, and learn in the process what other issues we need to take into consideration (for example, the space the algorithm uses, and whether the data is already sorted or nearly sorted).
The class DataSet represents one set of data to be
sorted. It knows the size of the data set, whether it is a sequential
subset of the original data or a randomly selected set of data. It
provides an iterator that generates for the sorting algorithm all
elements in this data set.
The class TestData generates all DataSets we will
use, so that we do not have to repeat this process, and also to make
sure that all algorithms will use sort the same data. This way we can
conduct 'controlled' experiments -- comparing outcomes when solving
the same problem.
The class TimerTests provides a framework for conducting
timing experiments. It contains a field that is an instance of
TestData so we do not have to
read the file citiesdb.txt of 29470 items for every test.
The method runOneTest runs one test of a sorting
algorithm. It consumes a sorting algorithm (an instance of
ASortAlgo) and an instance of DataSet. These two
pieces of data determine what is the data to be sorted, how large it
is, whether it is random or sequential, which algorithm is
used, and which comparator is used. It runs the sorting algorithm with
a stopwatch and produces the timing result.
Finally, the method allTests runs timing tests for all the
selected
combinations of sorting algorithms, comparators, and datasets and
collects the results into an ArrayList of Results.
Design the classes that implement the Java Comparator
interface and allow us to compare two cities by their zip codes
(class ComparatorByZip) and by longitude (class
ComparatorByLongitude).
Study the design of the class Result that holds the results
of the timing
tests. For each test we want to remember that the name of the test (for
example "Insertion sort with ArrayList"), the size of the data that we
sorted, whether it was sequentially or randomly selected data, and the
time it took to run the algorithm.
The method runATest in the
class TimerTests modifies the method runOneTest to
produce an instance of the Result.
Modify the method toString in the class Result to
produce a String that represents the
result formatted the way you would like to see the results.
The method runAllTests that consumes an
ArrayList of instances of SortAlgorithm, an
ArrayList of instances of Comparators, and the
instance of TestData, and runs the timing tests for each
algorithm, using each
of the comparators, using both, sequential and random data. The
results are produced as an ArrayList of
Results.
Run all possible tests. Make a note of those that fail. Choose a few at a time (for example all algorithms and comparators for a given dataset) and record the results into a text file or into a spreadsheet.
Look at the results of the timing tests and see what you can learn about the different ways to sort data.
If one of the algorithms takes too much time or space, you may eliminate it from further trials on larger datasets. However, try to understand why that may be hapenning.
You may also modify the way the dataset is initialized. For example, you may want to see how your algorithm performs on sorted data.
Present both the numerical
results, and your comments about the meaning of the results in a
professionally designed format -- possibly
with
charts. We care both about the results and about the way you
present them and explain what you learned from them.