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# CS 201 Homework Assignment 4 solution

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CS 201
Homework Assignment 4

In this homework, you will work on an extended version of the HPAir problem that we studied in the
class, which is also explained in Section 6.4 in your text book (Carrano’s book, 6’th edition). In this
assignment, we will provide you with a directed flight graph that shows the connections between cities.
A connection between two cities consists of a “flight id” and a “cost”. By using this flight graph, your
program must find all possible paths (sequences of flights) between the given departure and destination
cities

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CS 201
Homework Assignment 4

In this homework, you will work on an extended version of the HPAir problem that we studied in the
class, which is also explained in Section 6.4 in your text book (Carrano’s book, 6’th edition). In this
assignment, we will provide you with a directed flight graph that shows the connections between cities.
A connection between two cities consists of a “flight id” and a “cost”. By using this flight graph, your
program must find all possible paths (sequences of flights) between the given departure and destination
cities. It also should find the least cost path among all paths. A sample graph is shown in Figure 1.
R P
X Q
W S
T
Y
Z
9,500
2,150
3,200
1,100
7,400
10,550
4,250
5,300 6,350
8,450
11,600
Figure 1: Sample flight graph.
In Figure 1, each vertex corresponds to a city and each edge represents a flight between two cities. Each
edge has a flight id and a cost. For example, in Figure 1, the red colored edge’s id is “1” and its cost is
“100”. The graph can be stored by using adjacency lists as described in the Carrano book or by using an
adjacency matrix where the rows and columns correspond to individual cities. Given this graph, when
the departure city is selected as “P” and the destination city is selected as “Z”, your program must find
the paths “P → R → Z”, “P → W → Y → Z”, and “P → W → Y → R → Z”, and since the second path has a
cost of 1050, it is selected as the least cost path.
We will provide you with three files: cityFile, flightFile, and requestFile. The “cityFile” includes
the names of all cities in the flight graph. Each line has exactly one city name. The file for the example
graph is:
P
Q
R
S
T
W
X
Y
Z
City names can have any number of letters and can include spaces (e.g., Los Angeles). They can be
given in an arbitrary order (i.e., not necessarily in alphabetical order).
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The “flightFile” includes the edge list of the flight graph where each line describes an edge with its
origin city, destination city, flight id, and cost, separated by commas. The file for the example graph is:
P,W,1,100
R,X,2,150
Q,X,3,200
W,S,4,250
S,T,5,300
T,W,6,350
W,Y,7,400
Y,R,8,450
P,R,9,500
Y,Z,10,550
R,Z,11,600
The flights can be given in an arbitrary order (i.e., not necessarily sorted according to flight id or cost).
Both flight ids and costs can be assumed to be positive integers.
The “requestFile” includes a pair of city names in each line. First city name is assumed to be the
departure city and the second city name is assumed to be the destination city. Each line has exactly one
pair of cities. An example is:
P,Z
Q,X
Your solution must be implemented in a class called FlightMap. Below is the required public part of
the FlightMap class. The interface for the class must be written in a file called FlightMap.h and its
implementation must be written in a file called FlightMap.cpp. You can define additional public and
private member functions and data members in this class. You can also define additional classes in your
solution.
class FlightMap {
public:
FlightMap( const string cityFile, const string flightFile );
~FlightMap();
void displayAllCities() const;
void displayAdjacentCities( const string cityName ) const;
void displayFlightMap() const;
void findFlights( const string deptCity, const string destCity ) const;
void findLeastCostFlight( const string deptCity, const string destCity )
const;
void runFlightRequests( const string requestFile ) const;
};
The member functions are defined as follows:
FlightMap: Constructor. Reads the flight graph information from the files cityFile and flightFile
given as parameters and stores the flight graph. The graph can be stored by using adjacency lists as
described in the Carrano book or by using an adjacency matrix where the rows and columns correspond
to individual cities.
displayAllCities: Displays all cities in the flight graph.
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displayAdjacentCities: Displays the cities adjacent to the given city (i.e., all cities that have a flight
coming from the given city).
displayFlightMap: Displays all adjacent cities for all cities in the graph. In other words, this function
displays the whole flight graph.
findFlights: Finds and displays all paths (sequences of flights) from the departure city to the destination city. If there is no such path, displays a warning message.
findLeastCostFlight: Finds and displays all paths and identifies the least cost path from the departure city to the destination city. If there are multiple paths that have the same lowest cost, only one of
them will be displayed (any one of them is acceptable).
runFlightRequests: For each request given in the requestFile, finds and displays all paths from the
departure city to the destination city as well as the least cost path.
Here is an example test program that uses this class and the corresponding output. We will use a similar
program to test your solution so make sure that the name of the class is FlightMap, its interface is in
the file called FlightMap.h, and the required functions are defined as shown above.
Example test code:
#include “FlightMap.h”
int main() {
FlightMap fm( “files/cityFile.txt”, “files/flightFile.txt” );
cout << “The list of the cities that HPAir serves is given below:” << endl;
fm.displayAllCities();
cout << endl;
cout << “The cities adjacent to W are:” << endl;
cout << endl;
cout << “The whole flight map is shown below:” << endl;
fm.displayFlightMap();
cout << endl;
fm.findFlights( “W”, “Z” );
cout << endl;
fm.findFlights( “S”, “P” );
cout << endl;
fm.findLeastCostFlight( “Y”, “Z” );
cout << endl;
fm.findLeastCostFlight( “P”, “X” );
cout << endl;
fm.runFlightRequests( “files/requestFile.txt” );
return 0;
}
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Output of the example test code:
The list of the cities that HPAir serves is given below:
P, Q, R, S, T, W, X, Y, Z,
The cities adjacent to W are:
W – Y, S,
The whole flight map is shown below:
P – R, W,
Q – X,
R – Z, X,
S – T,
T – W,
W – Y, S,
X –
Y – Z, R,
Z –
Request is to fly from W to Z:
Flight #7 from W to Y Cost: 400 TL
Flight #8 from Y to R Cost: 450 TL
Flight #11 from R to Z Cost: 600 TL
Total Cost ………. 1450 TL
Flight #7 from W to Y Cost: 400 TL
Flight #10 from Y to Z Cost: 550 TL
Total Cost ………. 950 TL
Request is to fly from S to P:
Sorry. HPAir does not fly from S to P
Request is to fly from Y to Z:
Flight #8 from Y to R Cost: 450 TL
Flight #11 from R to Z Cost: 600 TL
Total Cost ………. 1050 TL
Flight #10 from Y to Z Cost: 550 TL
Total Cost ………. 550 TL
A least cost path from Y to Z is Y – Z and its cost is 550 TL
Request is to fly from P to X:
Flight #1 from P to W Cost: 100 TL
Flight #7 from W to Y Cost: 400 TL
Flight #8 from Y to R Cost: 450 TL
Flight #2 from R to X Cost: 150 TL
Total Cost ………. 1100 TL
Flight #9 from P to R Cost: 500 TL
Flight #2 from R to X Cost: 150 TL
Total Cost ………. 650 TL
A least cost path from P to X is P – R – X and its cost is 650 TL
Request is to fly from P to Z:
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Flight #1 from P to W Cost: 100 TL
Flight #7 from W to Y Cost: 400 TL
Flight #8 from Y to R Cost: 450 TL
Flight #11 from R to Z Cost: 600 TL
Total Cost ………. 1550 TL
Flight #1 from P to W Cost: 100 TL
Flight #7 from W to Y Cost: 400 TL
Flight #10 from Y to Z Cost: 550 TL
Total Cost ………. 1050 TL
Flight #9 from P to R Cost: 500 TL
Flight #11 from R to Z Cost: 600 TL
Total Cost ………. 1100 TL
A least cost path from P to Z is P – W – Y – Z and its cost is 1050 TL
Request is to fly from Q to X:
Flight #3 from Q to X Cost: 200 TL
Total Cost ………. 200 TL
A least cost path from Q to X is Q – X and its cost is 200 TL
Below is an example code segment for reading from text files. You can modify it according to the specific
format of the text files in this assignment.
//Declare variables
string fileName = “test.txt”;
string text;
ifstream inputFile;

//Open the stream for the input file
inputFile.open( fileName.c_str(), ios_base::in );

//Continue until the end of the file
while ( inputFile.eof() == false ) {
//Read until a comma
getline( inputFile, text, ’,’ );
//Read until the end of the line
getline( inputFile, text, ’\n’ );
}

//Close the input file stream
inputFile.close();
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IMPORTANT NOTES:
Do not start your homework before reading these notes!!!
Output message for each operation should match the format shown in the output of the
example code.
1. You MUST use the nonrecursive solution using a stack to implement the search algorithm for
finding the paths between the cities as discussed in the class. You will get no points if you use any
other algorithm for the solution of the search problem. You can use other data structures to help
with your implementation but the main search algorithm must be implemented using a stack.
2. You MUST use your own implementation of a stack in this assignment. In other words, you cannot
use any existing stack code from any other source. However, you can adapt the stack codes in the
Carrano book or in our lecture slides.
3. You are NOT ALLOWED to modify the given parts of the class definition. Note that you can
define additional public and private member functions and data members in the given class. You
can also define additional classes in your solution.
4. You are NOT ALLOWED to use any global variables or any global functions.
5. Your code MUST NOT have any memory leaks. You will lose points if you have memory leaks in
your program even though the outputs of the operations are correct.
6. Make sure that each file that you submit (each and every file in the zip archive) contains your
name, section, and student number at the top as comments.
1. This assignment is due by 23:59 on December 28, 2020.
2. You MUST have separate interface and implementation files (i.e., separate .h and .cpp files) for
your classes. We will test your implementation by writing our own driver .cpp file which will
include your header file. For this reason, your class’ name MUST be “FlightMap” and your files’
name MUST be “FlightMap.h” and “FlightMap.cpp”. You should upload these two files (and
any additional files if you wrote additional classes in your solution) as a single zip file. In this zip
file, there should not be any file containing the main function. The name of this zip file should
be secX_Firstname_Lastname_StudentID.zip where X is your section number. The submissions
that do not obey these rules will not be graded. We also recommend you to write your own driver
file to test each of your functions. However, you MUST NOT submit this test code (we will use
our own test code). In other words, your submitted code should not include any main function.
3. No hard copy submission is needed. The standard rules about late homework submissions apply.
4. You are free to write your programs in any environment (you may use either Linux or Windows).
Yet, we will test your programs on “dijkstra.ug.bcc.bilkent.edu.tr” and we will expect your programs
to compile and run on the dijkstra machine. If we could not get your program properly work on
the dijkstra machine, you would lose a considerable amount of points. Therefore, we recommend
you to make sure that your program compiles and properly works on dijkstra.ug.bcc.bilkent.edu.tr
before submitting your assignment.
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