Description
1 Overview
For this assignment you need to write a program that finds a path between two specified points
in a road map, if such a path exists. The road map has 3 kinds of roads: public roads that have
no cost for using them, private roads that have a positive cost or toll for using them, and reward
roads that pay the user a certain amount of money for using them (as the user of such roads is
required to perform a certain task, like cleaning the road). Your program will receive as input a file
with a description of the road map, the starting point s, the destination e, an amount of money k
that the program initially has for paying for the use of private roads, the cost of using each private
road, and the amount gained by using a reward road. Your program will try to find a path from s
to e that can be traversed with the given amount of money plus the money earned from using the
reward roads.
Your program will store the road map as an undirected graph. Every edge of the graph represents
a road and every node represents either the intersection of two roads or the end of a road. There
are two special nodes in this graph denoting the starting point s and the destination e. A modified
depth first search traversal, for example, can be used to find a path as required.
2 Classes to Implement
You are to implement at least six Java classes: Node, Edge, GraphException, Graph, MapException,
and RoadMap. You can implement more classes if you need to, as long as you follow good program
design and information-hiding principles.
You must write all code yourself. You cannot use code from the textbook, the Internet, other
students, or any other sources. However, you are allowed to use the algorithms discussed in class.
For each one of the classes below, you can implement more private methods if you want to, but
you cannot implement additional public methods.
2.1 Node
This class represent a node of the graph. You must implement these public methods:
• Node(int name): This is the constructor for the class and it creates a node with the given
name. The name of a node is an integer value between 0 and n − 1, where n is the number
of nodes in the graph.
• setMark(boolean mark): Marks the node with the specified value, either true or false.
This is useful when traversing the graph to know which vertices have already been visited.
• boolean getMark(): Returns the value with which the node has been marked.
• int getName(): Returns the name of the vertex.
2.2 Edge
This class represents an edge of the graph. You must implement these public methods:
• Edge(Node u, Node v, int type): The constructor for the class. The first two parameters
are the endpoints of the edge. The last parameter is the type of the edge, which for this
project can be either 0 (if the edge represents a public road), 1 (if the edge represents a
private road), or -1 (if the edge represents a reward road).
• Node firstEndpoint(): Returns the first endpoint of the edge.
• Node secondEndpoint(): Returns the second endpoint of the edge.
• int getType(): Returns the type of the edge.
2.3 Graph
This class represents an undirected graph. You must use an adjacency matrix or an adjacency list
representation for the graph. For this class, you must implement all the public methods specified in
the provided GraphADT interface plus the constructor. These public methods are described below.
• Graph(n): Creates a graph with n nodes and no edges. This is the constructor for the class.
The names of the nodes are 0, 1, . . . , n−1.
• Node getNode(int name): Returns the node with the specified name. If no node with this
name exists, the method should throw a GraphException.
• insertEdge(Node u, Node v, int edgeType): Adds an edge of the given type connecting
u and v. This method throws a GraphException if either node does not exist or if in the
graph there is already an edge connecting the given nodes.
• Iterator incidentEdges(Node u): Returns a Java Iterator storing all the edges incident
on node u. It returns null if u does not have any edges incident on it.
• Edge getEdge(Node u, Node v): Returns the edge connecting nodes u and v. This method
throws a GraphException if there is no edge between u and v.
• boolean areAdjacent(Node u, Node v): Returns true if nodes u and v are adjacent; it
returns false otherwise.
The last four methods throw a GraphException if u or v are not nodes of the graph.
2.4 RoadMap
This class represents the road map. A graph will be used to store the map and to try to find a
path from the starting point to the destination. For this class you must implement the following
public methods:
• RoadMap(String inputFile): Constructor for building a graph from the input file specified
in the parameter; this graph represents the road map. If the input file does not exist, this
method should throw a MapException. Read below to learn about the format of the input
file.
• Graph getGraph(): Returns the graph representing the road map.
• int getStartingNode(): Returns the starting node (this value and the next two values are
specified in the input file).
• int getDestinationNode(): Returns the destination node.
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• int getInitialMoney(): Returns the initial amount of money available to pay tolls.
• Iterator findPath(int start, int destination, int initialMoney): Returns a Java
Iterator containing the nodes of a path from the start node to the destination node as
specified above, if such a path exists. The amount specified in initialMoney plus the money
earned by passing through the reward roads must be enough to pay for all the private roads.
If the path does not exist, this method returns the value null. For example for the road map
described below the Iterator returned by this method should contain the nodes 0, 1, 5, 6,
and 10.
3 Implementation Issues
3.1 Input File
The input file is a text file with the following format:
SCALE
START
END
WIDTH
LENGTH
INITIAL BUDGET
TOLL
GAIN
RHRHRH· · ·RHR
HXHXHX· · ·HXH
RHRHRH· · ·RHR
HXHXHX· · ·HXH
…
RHRHRH· · ·RHR
Each one of the first eight lines of the input file contains one number:
• SCALE is the scale factor used to display the map on the screen. Your program will not use this
value. If the map appears too small on your screen, you must increase this value. Similarly,
if the map is too large, choose a smaller value for the scale.
• START is the starting vertex.
• END is the destination vertex.
• WIDTH is the width of the map. The roads of the map are arranged in a grid. The number of
vertical roads in each row of this grid is the width of the map.
• LENGTH is the length of the map, or the number of horizontal roads in each column of the
grid.
• INITIAL BUDGET is the initial amount of money available to pay for private roads.
• TOLL is the amount of money that needs to be paid to use a private road.
• GAIN is the amount of money received when using a reward road.
For the rest of the input file, R can be any of the following characters: ’+’ or ’X’. H could be
’X’, ’T’, ’C’, or ’F’. The meaning of the above characters is as follows:
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• ’+’: denotes either and intersection of two roads, or a dead end
• ’T’: denotes a private road (Toll required)
• ’F’: denotes a public road (Free to use)
• ’C’: denotes a reward road (Cash received from using it)
• ’X’: denotes a block of houses
Each line of the file (except the first eight lines) must have the same length because, as mentioned
above, the only road maps that we will consider are grid road maps. Here is an example of an input
file:
30
0
10
4
3
1
1
1
+F+X+T+
FXCXFXF
+T+T+F+
XXTXTXF
+F+T+T+
This input represents the following road map
starting point
destination
private road
road
reward
public road
For the above example, the initial amount of money available for paying tolls is 1 dollar; each
toll costs 1 dollar, and using a reward road earns 1 dollar.
3.2 Graph Construction
The road map is represented as a graph in which nodes are numbered consecutively, starting at
zero from left to right and top to bottom. For
8 9 10 11
4 5 6 7
0 1 2 3
starting point
destination
where dotted edges represent private roads, solid edges represent public roads, and wavy edges
represent reward roads. In the RoadMap class you need to keep a reference to the starting and
destination nodes.
3.3 Finding a Path
Your program must find any path from the starting vertex to the destination vertex that uses at
most the specified amount of money. If there are several such paths, your program might return
any one of them.
The solution can be found, for example, by using a modified DFS traversal. While traversing
the graph, your algorithm needs to keep track of the vertices along the path that the DFS traversal
has followed. If the current path has already used all available money to pay tolls, then no more
private-road edges can be added to it.
For example, consider the above graph and let the initial amount of money be 1. Assume
that the algorithm visits vertex 0, then 4, and then 5. As the algorithm traverses the graph, all
visited vertices get marked. While at vertex 5, the algorithm cannot next visit vertices 6 or 9, since
then two private roads would have been used by the current path at a total cost of 2. Hence, the
algorithm goes next to vertex 1. However, the destination cannot be reached from here, so the
algorithm must go back to vertex 5, and then back to vertices 4 and 0. Note that vertices 1, 5 and
4 must be unmarked when the algorithm steps back, as otherwise the algorithm will not be able
to find a solution. Next, the algorithm will move from vertex 0 to vertex 1, and then to 5. Since
edge (1, 5) represents a reward road, the algorithm earns 1 dollar, so the total amount of money
that the algorithm has is 2. The algorithm can then move to node 6 and then to 10 as now it can
pay for the two private roads. Therefore, the solution produced by the algorithm is: 0, 1, 5, 6,
and 10.
You do not have to implement the above algorithm if you do not want to. Please feel free to
design your own solution for the problem.
4 Code Provided
You can download from the course’s website the following files: TestDict.java, DrawMap.java,
Board.java, Path.java, GraphADT.java, and several image files. The main method is in class
Path.java , so to run your program you will type
Java Path input file
You can also type
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java Path input file delay
where delay is the number of milliseconds that the program will wait before drawing the next edge
of the solution.
You can use TestDict.java to test your implementation of the Graph.java class. You can
also download from the course’s website some examples of input files that we will use to test your
program.
5 Hints
Recall that the java class Iterator is an interface, so you cannot create objects of type Iterator.
The methods provided by this interface are hasNext(), next(), and remove(). An Iterator can
be obtained, for instance, from a Vector or Stack object by using the method iterator(). For
example, if your algorithm stores the path from the starting node to the destination in a Stack S,
then an iterator can be obtained from S by invoking S.iterator().
6 Coding Style
Your mark will be based partly on your coding style.
• Variable and method names should be chosen to reflect their purpose in the program.
• Comments, indenting, and white spaces should be used to improve readability.
• No unnecessary instance variables must be used in your code.
• All instance variables must be declared private, to maximize information hiding.
7 Marking
Your mark will be computed as follows.
• Program compiles, produces meaningful output: 2 marks.
• Tests for the Graph class: 4 marks.
• Tests for the RoadMap class: 4 marks.
• Coding style: 2 marks.
• Graph implementation: 4 marks.
• RoadMap implementation: 4 marks.
8 Handing In Your Program
You must submit an electronic copy of your program through OWL. Please DO NOT put your
code in sub-directories. Please DO NOT submit a .zip file or other compressed file containing
your code; submit the individual .java files.
You can submit your program more than once if you need to. We will take the latest program
submitted as the final version, and will deduct marks accordingly if it is late. Please send me an
email if you make multiple submissions so we can ensure that your last submission is marked.
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