CSC212 Lab 13 2014

--D. Thiebaut (talk) 11:19, 17 November 2014 (EST)

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For Tuesday's lecture, do Problem #1 and Problem #2.

Problem #1: DFS

• Create a new program called Graph1.java and copy the code from this page.
• Implement the DFS function, with the main DFS function calling a recursive helper DFSRecurse function.

Question 1

Make your new DFS start with a vertex of your choice, and display all the vertices it visits. Below is an example of the output for G.DFS( 0 ).

DFS starting on 0: 0, 1, 2, 4, 3, 7, 8, 5, 6,

Question 2

Same question, but this time make DFS print the edges of the graph it visits. Below is an example of the output for G.DFS(0).

DFS starting on 0:
visiting Edge (0)---(1)
visiting Edge (1)---(2)
visiting Edge (1)---(4)
visiting Edge (4)---(3)
visiting Edge (3)---(7)
visiting Edge (7)---(8)
visiting Edge (1)---(5)
visiting Edge (5)---(6)

Problem #2: Connected Components

• A graph is connected if there is a path from any vertex to any other vertex in the graph.
• Create a new method called isConnected( ) that is based on DFS, and that returns true if the graph is connected, and false otherwise.
• The graph created by the init1() method is connected. You will need to add a new method called, say, init2() that initializes the graph with several disconnected components. (Hints: You can probably remove some edges from the graph generated by init1() to get a graph with several components!)

Problem #3: GraphViz & Dot

• Add a method to your graph that will print the graph in dot language, as we did with trees a while back.
• Here's the dot version of the graph generated by init1():

graph G { 1 -- 0; 2 -- 1; 3 -- 0; 4 -- 1; 4 -- 3; 5 -- 1; 6 -- 5; 7 -- 3; 8 -- 4; 8 -- 7; }

• You can test your dot definition at this URL: http://sandbox.kidstrythisathome.com/erdos/

Problem #4: 6 degrees of Separation

• Have you ever heard of Kevin Bacon's degrees of separation? The idea is explained in this Wikipedia page.

• Interesting tidbit found on the same Wikipedia page:

While at the University of Virginia, Brett Tjaden created the Oracle of Bacon, a computer program that uses information on some 800,000 people from the Internet Movie Database (IMDb). The algorithm calculates "how good a center" an individual IMDb personality is, i.e. a weighted average of the degree of separation of all the people that link to that particular person.

There is an interesting graph shortest-path algorithm that you can try on the Oracle of Bacon Web site.

• Assume that we take 100 Hollywood stars and record the connections that they have had during the past year. This generates a graph shown below. Each number represents a Hollywood star. The list of stars and numbers is available here.

Question 1

Figure out a way to have your program output the Id of all the stars who are 1 degree away from Kevin Bacon.

Question 2

Make your program output the Ids of all the stars who are at most 4 degrees away from Kevin Bacon.

Question 3

Output all the Ids of the stars who are at an ∞ degree from Kevin Bacon.

Problem #5

To be provided later...