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# Assignment #6 Drawing one-stroke pictures

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Programming Assignment #6

Please list all sources in the table below including web pages which you used to solve or implement the
current homework.
Programming Assignment #6

The final challenge!
Congratulations! You just unlocked your final challenge! Tai Lung is ready for you. Are you?
• As part of this challenge, you should write a C++ program based on the graph data structure that can determine
if it is possible to draw a picture in one stroke, that is, without lifting a pen or retracing part of the picture
(excluding nodes).
• Use the pictures listed below and solve the challenge by hand. If you find a way to draw a picture with these
requirements, list the sequence of line segments where each line segment is represented by two numbered
endpoints (nodes). Can every picture be generated in one stroke?
Picture 1 Picture 2
Picture 3 Picture 4
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• The purpose of the exercise is to formulate the necessary and sufficient conditions for drawing one-stroke pictures. Those conditions allow you design an algorithm for determining the existence of a solution. Answer these
questions in your report:
– Determine for which group of pictures there are always solutions.
– Determine for which group of pictures there are no solutions.
– Determine for which group of pictures there exist solutions starting at one point and ending at the same
point. What kind of point could be selected as the start/end point in such a case?
– Determine for which group of pictures there exist solutions starting at one point and ending at a different
point. What kind of points could be selected as the start/end points in such a case?
– Eventually, provide the necessary and sufficient conditions for drawing one-stroke pictures.
• Hint for searching for solutions:
Picture 5 Picture 6
Notice that the output (1,2) → (2,3) → (3,1) is incorrect because does not contain all the line segments of this
pictures. You cannot continue drawing because retracing a line segment is not allowed. Your algorithm must be
able to go back to the vertex 2, and search for another edge to draw.
A correct output is a sequence of the line segments marked by its endpoints:
(1,2) → (2,4) → (4,5) → (5,2) → (2,3) → (3,1)
If possible, select the vertex 1 as your starting point; otherwise, you must start at another vertex to complete the
drawing.
Notice that a correct output is not unique, even if you select the same starting point.
• Need some help?
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Well if you are lost, you can try to run this pseudocode on Pictures 5 and 6:
Graph G;
Stack S;
verify that a solution exists;
select vertex u in G as the starting point and call Search(u);
print S as output if Search(u) returns true;
bool Function Search(u)
S.push(u);
if no edges available
return true;
else
for all adjacent vertices v of u in graph G
e = (u,v);
delete edge e from G;
f = Search(v);
if f is true
return true;
else
undo deleting: restore e by adding to G;
end if
end for
S.pop();
return false;
end if
end Function
Answer the following questions:
• What is the status of the stack S at the end of the function Search?
• If we apply this pseudocode to a picture that doesn’t actually have a solution, what will the output be?
Get a computer help!
• Write C++ code to find your solutions.
• In order to successfully complete this challenge, you need to use the graph data structure which helps you
organize information about a picture in order to implement it in C++.
– Input: an undirected connected graph G(V,E), with all the vertices numbered.
– Output: True/False
• The input pictures are stored in plain text files named graph1.data, …, graph6.data. This is a sample
of an input file for Picture 5:
4
5 6
1 2
2 3
3 1
2 4
4 5
5 2
The first line of the input file contains the number of vertices and the number of edges, respectively. The next
lines contain the endpoints of edges. Parse the input file (graph1.data, graph2.data, …) to obtain their
computer graph representation using the sequence of the input edges. You can use the adjacent matrix in this
assignment to store graphs.
• (20 points) Part 1 of the assignment: Implement a graph representation. It is due in the labs on April 17.
1. Create a graph data structure using the adjacency matrix representation.
2. Please read the textbook along with the supplementary material on the class webpage before you start
writing C++ code for the graph data structure.
3. Compile your program using the Linux machine command line:
c++ -std=c++14 *.cpp
or
make all
4. Run your program on each input file by executing
./main input_file
for example: ./main graph1.data
5. Display the output in the format vertex name followed by the list of adjacent vertices separated by -. This
is the illustration of the output for a graph corresponding to Picture 5.
1 – 2 – 3
2 – 1 – 3 – 4 – 5
3 – 1 – 2
4 – 2 – 5
5 – 2 – 4
• (10 points) Part 2 of the assignment: Use this graph data structure and determine the possibility to draw a
picture with one stroke. The algorithm should output True or False. Use the provided input files for testing.
• (5 points) If the algorithm outputs True, you need to find the starting vertex to draw a path. If possible, select
the vertex 1 as the starting vertex; otherwise, you must start at another vertex to complete the drawing.
• (25 points) Part 3 of the assignment: You need to find the starting vertex and a path to draw the graph in one
stroke. To check your program for correctness draw a graph based on the obtained output.
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Congratulations! You are almost there. Just one last bit. To complete the challenge, you will need to submit the
following.
1. (Total: 60 points) Your C++ source code with the header block including: your name, user name, section number
and e-mail address. Submit your tar file to eCampus not later than April 28 by midnight.
2. (40 points) A report which should consist of the following parts:
(a) The cover page with your (electronic) signature
(b) The description of the data structures implemented in your program
(c) The necessary and sufficient conditions for drawing one-stroke pictures.
(d) Description of the algorithm and its running time.
(e) The evidence of testing your program for correctness.
3. You will also be required to submit a hard copy of the report during your demonstration for this assignment in
the labs on April 29th.
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