Programming Assignment #3, CPS 100E, Fall 1996:
Sorting Linked Lists (20 points)

Bonus Due Date: Monday, November 4, midnight
Final Due Date: Friday, November 8, midnight

This assignment will provide practice with pointers, lists, and sorting.

Table of Contents

[ Introduction | Coding | Grading | Submitting ]

(A Makefile is accessible in ~ola/cps100e/linksort on the acpub system. Be sure to create a subdirectory linksort for this problem and to set the permissions for access by prof/uta/ta by typing fs setacl linksort ola:cps100e read.)

For net access and outside users files are accessible here:

You'll want to link to the directory containing literary works such as The Scarlet Letter, The Cask of Amontillado, and many of Shakespeare's plays. To do this on the acpub system type: ln -s ~ola/data data which will create a link to the data directory (the link is named data.) You can then type data/poe.txt to access the text by Edgar Allen Poe.

Introduction

For this assignment you'll read words from a file, store each word in one node of a linked list, and sort the linked lists using both quicksort and mergesort. You'll time the two sorting methods using different input files.

When reading words, you'll store each word once, so if the word the occurs 20 times in a file it will appear only once in the list of words you create. Words are white-space delimited (use the extraction operator >> to read) and should contain no leading or trailing punctuation.

back to table of contents

Coding/Algorithm

Your program should prompt for the name of a data file, read words from the file and store them in a list. The code below provides a start. You don't need to use classes for this program although you are welcome to do so. string word,filename; ifstream input; cout << "enter file name: "; cin >> filename; input.open(filename.cstr()); if (! input) { cout << "could not open file: " << filename << endl; exit(1); } while (input >> word) { StripPunc(word); // check if word already in list // add to front of list if not already in list } The function StripPunc is accessible by #including "strutils.h". You'll probably want to write a function to search for a word in a linked list.

After reading all the words into a linked list you should sort the list using Quicksort and time how long the sort takes. The class CTimer shown below is accessible by #including "ctimer.h".

CTimer timer; timer.Start(); QuickSort(first,last); timer.Stop(); cout << "time to quick sort = " << timer.ElapsedTime() << endl; (first points to the first node, last points to the last node.)

To quick sort a list, first partition using the first node as the pivot node. Partition the list into two new lists: those nodes less than or equal to the pivot node and those nodes greater than the pivot node. Then sort the two sublists and join them together when done. Your code will be more efficient if you keep pointers to the first and last nodes of the sublists that result from partitioning since this will make joining the two lists simpler.

To merge sort a list, find the middle node and divide the list into roughly equal sized lists. Recursively sort the two lists then merge the two sublists back into one list by traversing each sorted sublist and moving the smaller node into the "new" sorted list.

Note that no new nodes are created once the words are read from the file, only pointers are re-arranged to sort the lists.

back to table of contents

Grading

You should be sure to test your program to ensure that it sorts correctly. You must also time the program using several data files. You should explain as best you can the results of the timings. This means you should try to present reasons for why some files are sorted faster with each sorting method.

You must provide timings and explanations of the timings in your README file for the following data files. You can supply additional data if it helps in evaluating the sorting methods.

This assignment is worth 20 points. Points will be awarded as follows:
Behavior Points
Sorts Correctly with Quicksort 5
Sorts Correctly with Mergesort 5
Coding Style 5
README, Explanation 5

Submission

You should create a README file for this and all assignments. All README files should include your name as well as the name(s) of anyone with whom you collaborated on the assignment and the amount of time you spent.

To submit your assignment, type:

submit100e linksort README linksort.cc Makefile ... Be sure to submit all source files.