MAT 7003 : Mathematical Foundations
(for Software Engineering)
J Paul Gibson, A207
[email protected]
http://www-public.it-sudparis.eu/~gibson/Teaching/MAT7003/
Graphs and Trees – Code to Detect Cycles
http://www-public.it-sudparis.eu/~gibson/Teaching/MAT7003/L2-GraphsAndTrees-CyclesSolution.pdf
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.1
Programming Exercise: check for cycles?
For any graph, such as G, node and
arc labelled, with directed arcs,
chose a textual (string)
representation.
Write a function/method/procedure
(in the programming language of
your choice) that reads the string
representation and returns true if the
given graph contains a cycle (loop)
NOTE: Checking for cycles is very important because many
graph algorithms work only if there are no cycles in the graph
(otherwise they may get into an infinite loop)
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.2
Programming Exercise: check for cycles?
Did Any Of You Re-use Code?
Search on-line
Library code
Your own libraries/packages
http://jgrapht.org/
/* ==========================================
* JGraphT : a free Java graph-theory library
* ==========================================
*
* Project Info: http://jgrapht.sourceforge.net/
* Project Creator: Barak Naveh (http://sourceforge.net/users/barak_naveh)
*
* (C) Copyright 2003-2008, by Barak Naveh and Contributors.
*/
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.3
Programming Exercise: check for cycles?
For all programming languages/IDEs you need to know how
to use libraries properly :
•Create your own library
•Copy (or link to) someone elses library
•Include libraries in a project
There are often many different ways of doing this. You should
know the advantages and disadvantages of each
Here, I will download the zip and add it to my Java libraries
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.4
Programming Exercise: check for cycles?
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.5
Programming Exercise: check for cycles?
Now I Can Write My Test Code
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.6
Programming Exercise: check for cycles?
Download the code from the website and load into Eclipse
Take note of:
•Original Code Source is properly referenced in documentaion/comments
•Use of Javadoc tool to generate documentation
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.7
Programming Exercise: check for cycles?
Execute the test code
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.8
Programming Exercise: check for cycles?
public static void testNoCycleGraph(){
DefaultDirectedGraph<String, DefaultEdge> graphNoCycle =
new DefaultDirectedGraph<String, DefaultEdge>(DefaultEdge.class);
String vertexA = "A";
String vertexB = "B";
String vertexC = "C";
graphNoCycle.addVertex(vertexA);
graphNoCycle.addVertex(vertexB);
graphNoCycle.addVertex(vertexC);
Quick Look At Code
graphNoCycle.addEdge(vertexA, vertexB);
graphNoCycle.addEdge(vertexB, vertexC);
System.out.println(graphNoCycle);
CycleDetector<String, DefaultEdge> cycleDetector =
new CycleDetector<String, DefaultEdge>(graphNoCycle);
Set<String> cycleVertices = cycleDetector.findCycles();
System.out.println("Cycle vertices are "+ cycleVertices);
boolean foundCycleFromA = cycleDetector.detectCyclesContainingVertex(vertexA);
boolean foundCycleFromB = cycleDetector.detectCyclesContainingVertex(vertexB);
System.out.println("Found cycle including A is "+ foundCycleFromA);
System.out.println("Found cycle including B is "+ foundCycleFromB);
}
2012: J Paul Gibson
T&MSP: Mathematical Foundations
MAT7003/L2-GraphsAndTreesCyclesSolution.9