# CSCI-1200 Homework 4 — Preference Lists solved

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## Description

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In this assignment you will write a program to manage the preferences and rankings between schools and
applicants who wish to enroll at those schools. Your program will handle several different operations: adding
a school and the ranking of students that the school is interested in admitting to their program, adding
a student and the ranking of schools that applicant is interested in attending, editing (adding/removing)
preferences, and printing the current state of these lists. Please carefully read the entire assignment before
We provide the code to parse an input file that calls the operations listed above. Furthermore, we provide
an implementation of the Gale-Shapley algorithm to compute an assignment of students to schools that
is satisfying to both the schools and the students. This famous problem is called the “Stable Marriage
Problem”, which refers to the original problem statement:
Given n men and n women, where each person has ranked all members of the opposite sex with a
unique number between 1 and n in order of preference, marry the men and women together such
that there are no two people of opposite sex who would both rather have each other than their
current partners. If there are no such people, all the marriages are “stable”.
This algorithm enjoys real-world application each year to the problem of assigning medical residents to
solution, see http://en.wikipedia.org/wiki/Stable_marriage_problem.
Input/Output
The input for the program will come from a file and the output will also go to a file. These file names are
specified by command-line arguments. Here’s an example of how your program will be called:
preferences.exe requests.txt results.txt
The form of the input is relatively straightforward and easy to read. Each request begins with a special
keyword. There are nine different requests, described below. You may assume the input file strictly follows
this format (i.e., you don’t need to worry about format error-checking).
erin_jones
john_smith
dave_roberts
insert_student_into_school_preference_list university_of_michigan joe_miller dave_roberts
print_school_preferences university_of_michigan
The examples above illustrate how a school’s preference lists are managed. The add_school request is
followed by a string that represents the school’s name (using _ instead of spaces), an integer that represents
the number of available slots in the program, an integer that represents the number of students that are
will initially be placed on their preference list, and followed by the names of those students as strings (again
using _ rather than spaces). After initial construction of a school’s list, the list may be expanded with the
insert_student_into_school_preference_list request, which takes the name of the school, the name of
the new student to be added, and the name of a student who is already on the list in front of which this new
student should be inserted. Finally, the current state of a school’s preference list can be printed with the
print_school_preferences command, which will result in the following text being written to the output
file for this example:
university_of_michigan preference list:
1. erin_jones
2. john_smith
3. joe_miller
4. dave_roberts
Somewhat similarly, the student preference list is initially constructed with the add_student request, which
is followed by a string representing the student’s name, an integer representing the number of schools in
the initial ranking, and the names of those schools. While schools may add students into their preference
ranking after initial construction, students have the opposite operation, students may cross off schools in
their preference list using the remove_school_from_student_preference_list command.
duke_university
university_of_michigan
university_of_california_san_francisco
remove_school_from_student_preference_list erin_jones university_of_california_san_francisco
print_student_preferences erin_jones
The above requests will result in the following text being added to the output file:
erin_jones preference list:
1. duke_university
2. university_of_michigan
The final set of requests pertains to the matching of students to schools using the Gale-Shapley algorithm:
perform_matching
print_school_enrollments
print_student_decisions
The matching algorithm proceeds through a series of rounds or iterations. In each round, each school that
has open slots in its program, makes an offer to the next student on their preference list. When a student
receives an offer, he/she compares this new offer to his/her previous best offer (if any), and if this offer is
better, tentatively accepts this new offer (and declines the previous offer). Otherwise, the offer is declined.
The algorithm terminates after a round in which no offers are made (because all schools have either filled
their slots or schools with openings have exhausted their preference list of applicants). The progression of
the algorithm can be monitored by examining a log of these offers:
—- ROUND 1 —-
university_of_michigan makes an offer to erin_jones
erin_jones tentatively accepts offer from university_of_michigan
duke_university makes an offer to john_smith
john_smith declines offer from duke_university
university_of_california_san_francisco makes an offer to erin_jones
erin_jones declines offer from university_of_california_san_francisco
—- ROUND 2 —-
university_of_michigan makes an offer to john_smith
john_smith tentatively accepts offer from university_of_michigan
duke_university makes an offer to erin_jones
erin_jones withdraws tentative acceptance of offer from university_of_michigan
erin_jones tentatively accepts offer from duke_university
university_of_california_san_francisco makes an offer to joe_miller
joe_miller declines offer from university_of_california_san_francisco
2
—- ROUND 3 —-
university_of_michigan makes an offer to joe_miller
joe_miller declines offer from university_of_michigan
university_of_california_san_francisco makes an offer to john_smith
john_smith declines offer from university_of_california_san_francisco
—- ROUND 4 —-
university_of_michigan makes an offer to dave_roberts
dave_roberts tentatively accepts offer from university_of_michigan
—- ROUND 5 —-
The full solution can be printed in two formats: by school or by student (both shown below). The enrollments
for each school are printed ordered alphabetically by school and then alphabetically by student. The student
decisions are printed ordered alphabetically by student. Note that for simplicity, we treat the name of each
school and each student as a single string (using _ rather than spaces), and define “alphabetically” for these
names as the standard simple ordering of strings.
student(s) who will be attending duke_university:
erin_jones
student(s) who will be attending university_of_california_san_francisco:
[2 remaining slot(s) in enrollment]
student(s) who will be attending university_of_michigan:
dave_roberts
john_smith
[1 remaining slot(s) in enrollment]
dave_roberts will be attending university_of_michigan
erin_jones will be attending duke_university
joe_miller has not received an acceptable offer
john_smith will be attending university_of_michigan
Sample input and output files are posted on the course web site. Please follow these examples exactly. In
particular note the error messages that are printed for attempted duplicate insertion or removal of elements
that are not in the preference list.
Assignment Requirements, Hints, and Suggestions
• You may not use vectors or arrays for this assignment. Use STL lists instead. You may not
use maps, or sets, or things we haven’t seen in class yet.
• We have provided a partial implementation of this program, focusing on input parsing and the implementation of the Gale-Shapley algorithm. There are member function calls to our versions of the
School and Student classes, so you can deduce how some of the member functions in our solution
work. You are strongly encouraged to examine this code carefully and follow the interfaces suggested
without modification to the provided code.
• In your README.txt file, provide an order notation analysis of each operation assuming m schools, s
slots per school, r rankings of students by each school, n students, and p preferences of schools by each
student.
• Do all of your work in a new folder named hw4 inside of your homeworks directory. Use good coding
style when you design and implement your program. Be sure to make up new test cases to fully test