HW6: Graph homework in Java


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Reading: Graph chapter in Carrano, lecture notes from Friday 4/25.
Please begin by downloading (posted here) and (which contains stubs for the functions you will write) and (which is similar to the test code we’ll use). Also, download graph.txt, graph2.txt, and graph3.txt, which are files defining particular graphs to play with. The test code loads one of these automatically. has a function to display information about the edges to you, called printAdjacencyMatrix(). Use this for sanity checking your graphs; the edge matrix should always be symmetric for the graphs in this assignment, because these graphs are undirected.
The code you’ll write will complete the stubs in The file already contains an init() method that lets you load in a graph from a file. Leave that alone. Write code to complete DepthFirstList, BreadthFirstList, DepthFirstSpanningTree, and BreadthFirstSpanningTree. All of these algorithms are well described in the text, and they are all closely related; get one of them to work and you are close to getting all 4. You will make them able to work from any starting vertex, not just vertex 0.
If you choose to go for extra credit, you can complete Prim’s minimum spanning tree algorithm (for 10% extra credit) or Dijkstra’s shortest path algorithm (for 15% extra credit). But be aware that extra credit work needs to be done without so much help from the TAs and LAs; they will have their hands full with the basics. (These two algorithms are discussed in the text, but not very clearly. If you find the book’s explanation of these somewhat ugly, the web may have some better sources.) For Prim’s, return a graph containing the edges for the minimum spanning tree. For Dijkstra, return an ArrayList (an array) of strings, which are either numbers (the path weight, if the nodes are connected) or the letter ‘-‘ if there is no path between the two nodes.
Next week, I will post some graphs and solutions so you can test your code against mine. We will test your code using the same test file, but we’ll use different graphs than graph.txt, graph2.txt, and graph3.txt. I’ll also post solutions for the graphs in graph.txt, graph2.txt, and graph3.txt so you can check your work.
Some hints on Java template classes can be found at these pages, which are a little bit better than Java’s help:
To add a new item to an ArrayList, use add(). This adds the item at the end.
To get an existing item in an ArrayList, use get(). To change an existing item in an ArrayList, use set().
To add a new item to a Deque, use addFirst() or addLast(). To remove an item, use removeFirst() or removeLast().
To add a new item (a pair) to a Map, use put(). Use get() to retrieve an item.

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