CS 216
Data Structures and Algorithms

Description

The focus is on the following algorithms and data structures:

• Graph

• Breadth-First Search

• Depth-First Search

• Dijkstra's Single-Source Shortest Path

Create a project called Graph with the required classes.

Visualization resources

Here is a useful visualization resource:

• BFS Visualization | DFS Visualization | Dijkstra Visualization

• at the top-left there are three radio buttons that display the graph as:
  • picture / diagram
  • adjacency list - for each vertex only the neighbors are listed
  • adjacency matrix - a full table for all pairs of vertices

  • this assignment will use adjacency-list representation

JUnit

This means that there won't be assertEquals. Instead each @Test method will look like a mini-main method and you will inspect the console to see if the output is correct.

[ To test individual components you can comment //@Test ]

Here is an example:

@Test
public void test_bfs()
{
    Graph graph = new Graph("undirected.txt");

    String[] labelsList = { "a", ... };

    for ( ... ) {
        System.out.println("Source: ?");
        GraphAlgos.bfs(graph, ?);
    }
}

@Test
public void test_dijkstra()
{
    Graph graph = new Graph("directed.txt");

    String[] labelsList = { "a", ... };

    for ( ... ) {
        System.out.println("Source: ?");
        GraphAlgos.dijkstra(graph, ?);
    }
}

@Test
public void test_dfs()
{
    Graph graph = new Graph("directed.txt");

    String[] labelsList = { "a", ... };

    for ( ... ) {
        System.out.println("Source: ?");
        GraphAlgos.dfs(graph, ?);
    }
}

Vertex Representation

Each vertex will have the following data members:

• the (string) label of the vertex in the graph

• the distance value for this vertex during the traversal (for BFS and DFS this is just the level of the vertex in the traversal, which is one greater than that of its parent/predecessor); see the Double API for useful constants

• the (vertex) parent/predecessor during the traversal (i.e. the vertex that inserted this vertex in the queue or last updated the distance value)

• the mark field that indicates whether this vertex has entered the processing pipeline

• Vertex(String theLabel) - creates a blank vertex with the given text and integer labels

• toString() - returns a string representation of this vertex in the following format:

  MyLabel:MyDist:MyParentLabel    i.e.    Hanover:15:NewOxford
  

  this will be used in BFS and DFS for printing information during the traversal

Edge Representation

The interface for the Edge class is:

• Egde(Vertex theSource, Vertex theTarget, double theWeight)
• Vertex getSource()
• Vertex getTarget()
• double getWeight()

Graph Representation

The graph data members:

• edge map - associates a vertex label with a list of edges

• vertex map - associates a vertex label with a vertex

• (the list of vertices will be available through the values of the edge map)

Here is the required interface for the Graph class:

Graph(String filename) Reads a graph from the file with the given filename (see Scanner API). Make sure to use the appropriate constructor to open the file. If Eclipse does not suggest adding try/catch, you are using the wrong Scanner constructor. Methods .next() and .nextDouble() will read a single string and a single double, respectively. Method hasNext() will determine when to stop. The files are formatted as follows: source target weight Test files are available here - save them in the main project folder (next to src/, bin/): directed.txt - small weighted, directed graph undirected.txt - small weighted, undirected graph tube.txt - the London subway

Graph() This constructor is not required, but you might use it initially if you are not sure whether you can read from a file. This is just a sequence of addEgde calls for each line in the file you want to test. public Graph() { // any intialization // for BFS load "undirected.txt" // addEdge("a", "b", 2); // addEdge("a", "f", 7); // addEdge("a", "g", 3); // addEdge("a", "b", 2); ... USE ONLY ONE OR THE OTHER // for Dijkstra/DFS load "directed.txt" // addEdge("a", "b", 4); // addEdge("a", "f", 2); // addEdge("b", "c", 3); .... }

void addEdge(String sourceLabel, String targetLabel, double weight) Adds an edge with the given weight from the vertex with the given source label to the vertex with the given target label. Make sure duplicate vertices are not created. In other words, if called multiple times with sourceLabel or targetLabel "Gettysburg" it should always use the same Vertex object for "Gettysburg".

Vertex getVertex(String label) Returns a Vertex object for the given label. It should ensure that vertices are constructed/setup properly.

List<Edge> getAdjacent(Vertex source) Returns an unmodifiable list of the edges that have the given vertex as their source. [ Initially ignore the unmodifiable part. Later see the relevant method in the Collections API. ]

Collection<Vertex> getVertices() Returns an unmodifiable collection of the vertices in the graph. [ Initially ignore the unmodifiable part. Later see the relevant method in the Collections API. ]

Graph Traversal (BFS, DFS)

a:0:* b:1:a f:1:a g:1:a c:2:b e:2:f i:2:f h:2:g d:3:c

a:0:* b:1:a c:2:b d:3:c e:4:d f:1:a

Dijkstra's Single-Source Shortest Path

F <--5-- D <--2-- G <--6-- C <--4-- A (total length 17)  

A --4--> C --6--> G --2--> D --5--> F

GraphExplorer - Running from Command Line

• Intially in main run the various algorithms with hardcoded input files and source vertices

• In the final version change main to use its command-line arguments from the String[] parameter:
  • first cell is the algorithm name
  • second cell is the file to use
  • third cell is the start vertex

• Make sure to run GraphExplorer at least one time before the next step. It is enough to print a simple message in the main method. Without this step there won't be a Launch Configuration.

• Create an executable JAR file that can be run as a standalone program. Follow steps 1-4 described here:

  Create Executable JAR in Eclipse

  In Step 4 choose GraphExplorer under Launch Configuration and Browse to the project's main folder (Graph/) and save the jar under the name gbcsmaps.jar .

cd   path/to/project/Graph    (go to correct project folder)
  
java  -jar  gbcsmaps.jar  -bfs  undirected.txt  c    (runs BFS starting at c)

java  -jar  gbcsmaps.jar  -dfs  directed.txt    d    (runs DFS starting at d)

java  -jar  gbcsmaps.jar  -dijkstra  tube.txt   CHARING_CROSS    (runs Dijkstra starting at Charing Cross)

but replace javaw with java if path is too long, hover over it with the mouse