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# Assignment Five: Graph Algorithms

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Programming Assignment Five: Graph Algorithms

I. Motivation
1. To give you experience in implementing a graph data structure using the adjacency list
representation.
2. To give you experience in implementing a few graph algorithms.
II. Programming Assignment
You will read from the standard input a description of a directed graph and then report three
things on that graph:

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## Description

Programming Assignment Five: Graph Algorithms

I. Motivation
1. To give you experience in implementing a graph data structure using the adjacency list
representation.
2. To give you experience in implementing a few graph algorithms.
II. Programming Assignment
You will read from the standard input a description of a directed graph and then report three
things on that graph:
1. The shortest path between a source node and a destination node specified in the input.
2. Whether the graph is a directed acyclic graph (DAG).
3. Determine the total weight of a minimum spanning tree (MST) of the graph when it is treated
as an undirected graph.
1. Input Format
The first line in the input specifies the number of nodes in the graph, ?. The nodes in the graph
are indexed from 0 to ? − 1. The second line specifies a source node 0 ≤ ? ≤ ? − 1 and the
third line specifies a destination node 0 ≤ ? ≤ ? − 1. You should report the shortest path from ?
to ?. Each subsequent line represents a directed edge by 3 numbers in the form:
<start_node> <end_node> <weight>
where both <start_node> and <end_node> are integers in the range [0, ? − 1],
representing the start node and the end node of the edge, respectively, and <weight> is a nonnegative integer representing the edge weight. Thus, the graph specified in this format is a
directed graph with non-negative edge weights.
An example of input is
4
1
3
0 1 5
1 2 3
2 3 4
3 1 6
It represents the following directed graph with the source node as Node 1 and the destination
node as Node 3:
0 1
2
3
5
3
4
6
s d
Typically, we will describe the graph in a file. However, since your program takes input from the
standard input, you need to use the Linux input redirection “<” on the command line to read the
graph from the file.
2. Output Specification
Your program writes to the standard output. It will first show the shortest path. Then, it will tell
whether the graph is a DAG or not. Finally, it will calculate the total weight of a MST of the
original graph when treated as an undirected graph.
a) Showing the shortest path
If there exists a path from the source node to the destination node, your program should print the
length of the shortest path. Specifically, it should print the following line:
Shortest path length is <length>
where <length> specifies the length of the shortest path. In the special case where the source
node is the same as the destination node, the shortest path length is 0.
If there exists no path from the source node to the destination node, your program should print:
No path exists!
b) Telling whether the graph is a DAG or not
If the graph is a DAG, your program should print:
The graph is a DAG
Otherwise, print:
The graph is not a DAG
c) Calculating the total weight of an MST
You should treat all the directed edges in the original graph as undirected edges, and obtain the
total edge weight of a minimum spanning tree for the undirected graph. If there exists a spanning
tree, your program should print the total edge weight of an MST. Specifically, it should print the
following line:
The total weight of MST is <total_weight>
where <total_weight> specifies the total edge weight of an MST.
If there exists no spanning tree, your program should print:
No MST exists!
For the example graph shown above, one valid output should be:
Shortest path length is 7
The graph is not a DAG
The total weight of MST is 12
III. Program Arguments and Error Checking
Your program takes no arguments. You do not need to do any error checking. You can assume
that all the inputs are syntactically correct.
IV. Implementation Requirements and Restrictions
 You must implement the graph data structure using the adjacency list representation.
 You must make sure that your code compiles successfully on a Linux operating system. You
are required to write your own Makefile and submit it together with your source code files.
Your compiled program should be named as main exactly.
 We highly encourage the use of the STL, such as vector, deque, map, algorithm, etc.,
for this project, with the exception of two prohibited features: The C++11 regular
expressions library (whose implementation in gcc 4.7 is unreliable) and the thread/atomics
libraries (which spoil runtime measurements). Do not use other libraries (e.g., boost, pthreads,
etc).
 Output should only be done where it is specified.
V. Hints on Data Structure
You may want to define the following three abstract data types: node, edge, and graph.
VI. Testing
We have supplied three input files g1.in, g2.in, and g3.in for you to test your program.
The outputs of our program for these three inputs are also provided. They are g1.out, g2.out,
and g3.out. All these files are located in the Programming-Assignment-Five-Related-Files.zip.
To do the test, type a similar command to the following into the Linux terminal once your
program has been compiled:
./main < g1.in > test.out
diff test.out g1.out
If the diff program reports any differences at all, you have a bug.
These are the minimal amount of tests you should run to check your program. Those programs
that do not pass these tests are not likely to receive much credit. You should also write other
different test cases yourself to test your program extensively.
VII. Submitting and Due Date
You should submit all the related .h files, .cpp files, and the Makefile via the online
judgement system. The Makefile compiles a program named main. Please also include a pdf
file containing all of your source code. See announcement from the TAs for the details about
how to submit these files. The submission deadline is 11:59 pm on Dec. 16, 2017.
1. Functional Correctness
2. Implementation Constraints
3. General Style
4. Performance
Functional Correctness is determined by running a variety of test cases against your program,
checking your solution using our automatic testing program. We will grade Implementation
Constraints to see if you have met all of the implementation requirements and restrictions. For
example, we will check whether you implement the graph data structure using the adjacency list
representation. General Style refers to the ease with which TAs can read and understand your
program, and the cleanliness and elegance of your code. For example, if it is hard for the TAs to
General Style deductions. Part of your grade will also be determined by the performance of your
algorithm. We will test your program with some large test cases. If your program is not able to
finish within a reasonable amount of time, you will lose the performance score for those test
cases.Programming Assignment Five: Graph Algorithms
Out: Nov. 28, 2017; Due: Dec. 16, 2017.
I. Motivation
1. To give you experience in implementing a graph data structure using the adjacency list
representation.
2. To give you experience in implementing a few graph algorithms.
II. Programming Assignment
You will read from the standard input a description of a directed graph and then report three
things on that graph:
1. The shortest path between a source node and a destination node specified in the input.
2. Whether the graph is a directed acyclic graph (DAG).
3. Determine the total weight of a minimum spanning tree (MST) of the graph when it is treated
as an undirected graph.
1. Input Format
The first line in the input specifies the number of nodes in the graph, ?. The nodes in the graph
are indexed from 0 to ? − 1. The second line specifies a source node 0 ≤ ? ≤ ? − 1 and the
third line specifies a destination node 0 ≤ ? ≤ ? − 1. You should report the shortest path from ?
to ?. Each subsequent line represents a directed edge by 3 numbers in the form:
<start_node> <end_node> <weight>
where both <start_node> and <end_node> are integers in the range [0, ? − 1],
representing the start node and the end node of the edge, respectively, and <weight> is a nonnegative integer representing the edge weight. Thus, the graph specified in this format is a
directed graph with non-negative edge weights.
An example of input is
4
1
3
0 1 5
1 2 3
2 3 4
3 1 6
It represents the following directed graph with the source node as Node 1 and the destination
node as Node 3:
0 1
2
3
5
3
4
6
s d
Typically, we will describe the graph in a file. However, since your program takes input from the
standard input, you need to use the Linux input redirection “<” on the command line to read the
graph from the file.
2. Output Specification
Your program writes to the standard output. It will first show the shortest path. Then, it will tell
whether the graph is a DAG or not. Finally, it will calculate the total weight of a MST of the
original graph when treated as an undirected graph.
a) Showing the shortest path
If there exists a path from the source node to the destination node, your program should print the
length of the shortest path. Specifically, it should print the following line:
Shortest path length is <length>
where <length> specifies the length of the shortest path. In the special case where the source
node is the same as the destination node, the shortest path length is 0.
If there exists no path from the source node to the destination node, your program should print:
No path exists!
b) Telling whether the graph is a DAG or not
If the graph is a DAG, your program should print:
The graph is a DAG
Otherwise, print:
The graph is not a DAG
c) Calculating the total weight of an MST
You should treat all the directed edges in the original graph as undirected edges, and obtain the
total edge weight of a minimum spanning tree for the undirected graph. If there exists a spanning
tree, your program should print the total edge weight of an MST. Specifically, it should print the
following line:
The total weight of MST is <total_weight>
where <total_weight> specifies the total edge weight of an MST.
If there exists no spanning tree, your program should print:
No MST exists!
For the example graph shown above, one valid output should be:
Shortest path length is 7
The graph is not a DAG
The total weight of MST is 12
III. Program Arguments and Error Checking
Your program takes no arguments. You do not need to do any error checking. You can assume
that all the inputs are syntactically correct.
IV. Implementation Requirements and Restrictions
 You must implement the graph data structure using the adjacency list representation.
 You must make sure that your code compiles successfully on a Linux operating system. You
are required to write your own Makefile and submit it together with your source code files.
Your compiled program should be named as main exactly.
 We highly encourage the use of the STL, such as vector, deque, map, algorithm, etc.,
for this project, with the exception of two prohibited features: The C++11 regular
expressions library (whose implementation in gcc 4.7 is unreliable) and the thread/atomics
libraries (which spoil runtime measurements). Do not use other libraries (e.g., boost, pthreads,
etc).
 Output should only be done where it is specified.
V. Hints on Data Structure
You may want to define the following three abstract data types: node, edge, and graph.
VI. Testing
We have supplied three input files g1.in, g2.in, and g3.in for you to test your program.
The outputs of our program for these three inputs are also provided. They are g1.out, g2.out,
and g3.out. All these files are located in the Programming-Assignment-Five-Related-Files.zip.
To do the test, type a similar command to the following into the Linux terminal once your
program has been compiled:
./main < g1.in > test.out
diff test.out g1.out
If the diff program reports any differences at all, you have a bug.
These are the minimal amount of tests you should run to check your program. Those programs
that do not pass these tests are not likely to receive much credit. You should also write other
different test cases yourself to test your program extensively.
VII. Submitting and Due Date
You should submit all the related .h files, .cpp files, and the Makefile via the online
judgement system. The Makefile compiles a program named main. Please also include a pdf
file containing all of your source code. See announcement from the TAs for the details about
how to submit these files. The submission deadline is 11:59 pm on Dec. 16, 2017.
1. Functional Correctness
2. Implementation Constraints
3. General Style
4. Performance
Functional Correctness is determined by running a variety of test cases against your program,
checking your solution using our automatic testing program. We will grade Implementation
Constraints to see if you have met all of the implementation requirements and restrictions. For
example, we will check whether you implement the graph data structure using the adjacency list
representation. General Style refers to the ease with which TAs can read and understand your
program, and the cleanliness and elegance of your code. For example, if it is hard for the TAs to